Year 1 M Science Answers Page

Day 2

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. Organisms are living things.
  2. All living organisms need energy and resources to carry out life processes; are composed of one or more cells; respond and adapt to their environment; reproduce and grow and develop.
  3. All animals must eat plants or other animals in order to obtain energy and building materials.
    Plants use energy from the sun to make their “food” through the process of photosynthesis.
    Mushrooms and other fungi obtain energy from other organisms.
  4. Cells are the smallest unit of living things.
  5. Answers will vary. Fire does not have qualities of living organisms.

Day 3

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. The integumentary system is the organ system that includes the skin, hair, and nails.
  2. The cells at the bottom of the epidermis are always dividing by mitosis to form new cells. The new cells gradually move up through the epidermis toward the surface. As they move, they produce tough, fibrous keratin. By the time the cells reach the surface, they have filled with keratin and died. The dead cells are gradually shed from the surface of the epidermis and replaced by other dead cells that move up from below.
  3. Answers may vary. Sample answer: Three functions of the skin are preventing loss of water from the body, keeping microorganisms out of the body, and helping maintain a constant body temperature.
  4. Sebaceous glands secrete oily sebum, which spreads out over hairs and the skin surface. The sebum waterproofs the hair and skin and helps to prevent them from drying out. Sweat glands secrete salty sweat, which spreads out over the skin surface. When the sweat evaporates, it takes some of the heat from the body, so it helps keep the body cool.
  5. Any cut to the skin that penetrates the dermis is likely to be painful because there are many nerve endings in this layer of the skin. Hair and nails consist only of dead cells, so cutting them does not cause any pain.
  6. The epidermis is the outer layer of skin. It consists almost entirely of epithelial cells. The only skin structures it contains are melanocytes, which are cells that produce melanin. The dermis is the inner layer of skin. It consists of connective tissue. It also contains most skin structures, including blood vessels, nerve endings, hair follicles, and sebaceous and sweat glands.
  7. Melanocytes are special cells at the bottom of the epidermis that produce the brown pigment called melanin. Melanin in the epidermis absorbs ultraviolet light so it can’t reach the dermis and damage this layer of skin and its structures.

Day 5

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. Muscles are the main organs of the muscular system. They are composed primarily of long, thin cells called muscle fibers. Muscle fibers contain many organelles, known as myofibrils, which allow muscles to contract.
  2. Tendons are tough connective tissues that anchor skeletal muscles to bones throughout the body.
    When the muscles contract, they pull on the bones to which they are attached by tendons, and this allows movement.
  3. Public service announcements may vary but should argue convincingly and correctly why regular exercise is important for healthy muscles.
  4. Within myofibrils of a muscle’s muscle fibers, myosin filaments use energy from ATP to pull on actin filaments. This causes the actin filaments to slide over the myosin filaments and shorten sections of the myofibrils. This process occurs all along many myofibrils and in many muscle fibers, causing the fibers to shorten and the muscle to contract.
  5. Sample answer: The three types of muscle tissues are cardiac, smooth, and skeletal muscle tissues. All three types consist mainly of cells called muscle fibers, but their arrangement differs.
    In cardiac and skeletal muscle tissues, the muscle fibers are arranged in bundles, causing these muscle tissues to be striated, or striped. In smooth muscle tissue, the fibers are arranged in sheets rather than bundles, so smooth muscle tissue is not striated. The three types of muscle tissues differ in how they are controlled. Skeletal muscle tissue is under conscious control. Cardiac and smooth muscle tissues are not under conscious control. The three types of muscle tissues also differ in where they are found. Cardiac tissue is found only in the walls of the heart. Smooth muscle tissue is found in the walls of other internal organs such as the stomach. Skeletal muscle tissue is attached to bones of the skeletal system.
  6. Muscles can only contract. They can’t actively lengthen. Therefore, to move bones back and forth at joints, skeletal muscles must work in pairs. For example, the bicep and triceps muscles of the upper arm work as a pair. When the bicep muscle at the front of the upper arm contracts, it bends the arm at the elbow. When the triceps muscle at the back of the upper arm contracts, it straightens the arm.

Day 7

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. Components of the skeletal system include bones, cartilage, and ligaments.
  2. Answers may vary. Sample answer: Three functions of the skeletal system include supporting and shaping the body, protecting internal organs, and allowing the body to move.
  3. In the fetus, the skeleton starts out consisting entirely of cartilage. The relatively soft cartilage gradually changes to hard bone through ossification. At birth, several areas of cartilage remain, including the ends of the long bones in the arms and legs. This allows these bones to keep growing in length during childhood. By the late teens or early twenties, all of the cartilage has been replaced by bone. Bones cannot grow in length after this point has been reached. However, bones can continue to grow in width. They are stimulated to grow thicker when they are put under stress by muscles.
  4. Three types of joints based on the degree of movement they allow are immovable joints, which do not allow the bones to move at all; partly movable joints, which allow very limited movement; and movable joints, which allow the greatest movement. Examples of immovable joints are the joints between the bones of the skull. Examples of partly movable joints are the joints between the bones of the rib cage. Examples of movable joints are the shoulders, elbows, and knees.
  5. Weight-bearing exercise causes muscles to put stress on bones. This stimulates the bones to grow wider and stronger. Therefore, weight-bearing exercise might slow down the loss of bone minerals and reduce the risk of developing osteoporosis.
  6. Tables may vary, e.g. a sample table might include a comparison of location and function of tissues.
  7. Fractures are cracks or breaks in bone. They occur when too much stress is placed on bone.
    Sprains are strains or tears in ligaments. They occur when ligaments are twisted or stretched too far.

 

Day 11

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. The body needs food for energy, building materials, and substances that control body processes.
  2. A nutrient is any substance that the body needs. Types of nutrients that can provide the body with energy are carbohydrates, proteins, and lipids.
  3. Functions of protein in the diet include building muscles, controlling body processes, fighting infections, and carrying substances in the blood.
  4. Carbohydrates provide 4 Calories of energy per gram, so the 20 grams of carbohydrates in an apple provide 80 Calories of energy.
  5. Macronutrients and micronutrients are two general categories of nutrients. Macronutrients are nutrients the body needs in relatively large amounts, whereas micronutrients are nutrients the body needs in relatively small amounts. Macronutrients include carbohydrates, proteins, lipids, and water. Except for water, they all provide energy to the body. Micronutrients include minerals and vitamins. They do not provide energy to the body but are needed for other purposes.
  6. You need fiber to help keep sugar and lipids at normal levels in the blood. You also need fiber to help keep food waste moist so it can pass easily out of the body.
  7. Water is considered a nutrient because it is a substance that the body needs. Cells are mostly water and can’t survive without it.

 

Day 12

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. The GI, or gastrointestinal, tract is a long tube that starts at the mouth and ends at the anus. It includes the mouth, esophagus, stomach, small intestine, and large intestine
  2. In the mouth, the teeth break food into smaller pieces (mechanical digestion) and enzymes in saliva start breaking down starches to sugars (chemical digestion). The only role of the esophagus is to pass food from the mouth to the stomach. In the stomach, the churning of the stomach completes the mechanical digestion of food. Enzymes in the stomach continue chemical digestion. For example, the enzyme pepsin starts breaking down proteins into amino acids.
  3. Two functions of the large intestine are eliminating food waste as feces and providing a habitat for helpful bacteria.
  4. Answers may vary. Sample answer: Three foods that commonly cause food allergies are milk, shellfish, and nuts.
  5. Sample answer: You could reduce the risk of foodborne illness on a picnic by keeping cold foods cold and hot foods hot. This will slow the growth of bacteria in the foods. You could keep cold foods in an ice chest until you are ready to eat them. Hot foods could be kept in a thermos container.
  6. Enzymes are proteins that speed up chemical reactions. Digestive enzymes speed up the chemical reactions of digestion. Chemical digestion could not take place without digestive enzymes.
    Examples may vary. Sample answer: Examples of digestive enzymes are: amylase, which is produced in the mouth and helps digest carbohydrates; and pepsin, which is produced in the stomach and helps digest proteins.
  7. Most of the absorption of nutrients takes place in the small intestine. Nutrients are absorbed across the inner surface of the small intestine into blood vessels. Villi are tiny projections that cover the inner surface of the small intestine. They greatly increase the surface area across which absorption can take place. Each villus contains tiny capillaries to absorb the nutrients.

Day 25

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. Blood is a liquid tissue that consists of watery plasma and three types of blood cells.
  2. The main function of blood is transporting substances to cells throughout the body.
  3. Answers may vary. Sample answer: Two diseases of the blood are anemia and leukemia. Anemia is a disease that occurs when there is not enough hemoglobin (or iron) in the blood to carry adequate oxygen to cells. Possible causes of anemia include excessive blood loss and lack of iron in the diet. Leukemia is a type of cancer in which bone marrow produces abnormal white blood cells that can’t fight infections. Leukemia is thought to be caused by a combination of genetic and
    environmental factors.
  4. Sample answer: It might be necessary to determine your ABO blood type if you needed a blood transfusion because of an injury or surgery. It is safe to receive a transfusion only if the donated blood lacks the same antigens that your own blood is lacking.
  5. If you have type O blood, you can safely receive only type O blood. The other blood types (A, B, and AB) have antigens not found in your blood. Receiving blood of these types would cause your red blood cells to clump together, or agglutinate.
  6. Red blood cells are more numerous than white blood cells. Red blood cells are disc shaped, whereas white blood cells are sphere shaped. Red blood cells carry oxygen in the blood, whereas white blood cells defend the body.
  7. Antigens are proteins on the surface of red blood cells. The particular antigens on the cells determine a person’s blood type. For example, a person with A antigens on their red blood cells has blood type A in the ABO blood type system.

Day 27

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. The cardiovascular system consists of the heart, a network of blood vessels, and blood.
  2. The main function of the cardiovascular system is transporting substances throughout the body.
    Another function of the cardiovascular system is helping to regulate body temperature.
  3. Answers may vary. Sample answer: I think a highway system is a good analogy for the cardiovascular system because both a highway system and the cardiovascular system have the main purpose of transporting materials from one place to another. Blood vessels are also like the roads of a highway system. Both blood vessels and roads provide a network of pathways for the transport of materials.
  4. Both pulmonary and systemic circulation loops are part of the closed network of heart and blood vessels that make up the cardiovascular system. As blood circulates through the body, it travels first through one loop and then the other loop, over and over again. The pulmonary loop, which is shorter, carries blood back and forth between the heart and lungs, where the blood picks up oxygen. The systemic loop, which is longer, carries blood back and forth between the heart and the rest of the body, where blood releases oxygen to cells.

Day 31

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. The function of the respiratory system is to exchange gases with the outside air. It brings air containing oxygen into the body for the cells. It also releases carbon dioxide from the cells into the air.
  2. Respiration is the process of exchanging oxygen and carbon dioxide with the air. It involves breathing and transport of gases in the blood to and from cells. Cellular respiration is the “burning” of glucose for energy inside cells. It requires oxygen and produces carbon dioxide.
    These gases are exchanged between cells and blood and between blood and air in the process of respiration.
  3. Steps in the process of respiration include breathing (inhaling and exhaling), gas exchange between the air and blood, gas transport via the blood, and gas exchange between the blood and cells.
  4. Asthma is a disease in which bronchioles in the lungs periodically swell and fill with mucus.
    Symptoms of asthma may include difficulty breathing, wheezing, coughing, and chest tightness.
    An asthma attack may be triggered by allergies, strenuous exercise, stress, or another respiratory illness such as a cold.
  5. Posters will vary but should be relevant to teens and correctly identify dangers of smoking to respiratory system health, such as triggering asthma attacks and causing emphysema and lung cancer.
  6. Inhaling occurs when the diaphragm contracts. This increases the size of the chest, which decreases air pressure inside the lungs. The difference in air pressure between the lungs and outside air causes air to rush into the lungs. Exhaling occurs when the diaphragm relaxes. This decreases the size of the chest, which increases air pressure inside the lungs. The difference in air pressure between the lungs and outside air causes air to rush out of the lungs.
  7. The function of the lungs is to exchange oxygen and carbon dioxide between the blood and the air. The alveoli in the lungs are where this gas exchange takes place. Each alveolus is surrounded by a network of capillaries. When you inhale, air in the alveoli has a greater concentration of oxygen than does capillary blood. The difference in oxygen concentration causes oxygen to diffuse from the air in the alveoli into the blood in the capillaries. Carbon dioxide, in contrast, is more concentrated in the capillary blood than it is in the air in the alveoli. It diffuses in the opposite direction. It moves out of the blood and into the air in the alveoli.

Day 36

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. Excretion is any process in which excess water or waste is removed from the body.
  2. The organs of the excretory system include the large intestine, liver, skin, lungs, and kidneys.
  3. The urinary system is the organ system that filters waste products and excess water from the blood and excretes them from the body as urine. It includes two kidneys, two ureters, the urinary bladder, and the urethra. The kidneys filter blood and form urine. The ureters carry urine from the kidneys to the urinary bladder. The urinary bladder stores urine until it is excreted from the body through the urethra during urination.
  4. The kidneys of a person with kidney failure can’t filter blood to maintain  homeostasis.
    Hemodialysis is a medical procedure in which a patient’s blood is filtered through a machine. The machine does the work of the failing kidneys and keeps the patient alive.
  5. Blood with wastes enters each kidney through an artery, which branches into many capillaries. After passing through capillaries and being filtered, the clean blood leaves the kidney through a vein. Tiny structures called nephrons are the functional units of the kidneys. The part of each nephron called the glomerulus is where blood in the capillaries is filtered. Excess water and wastes are filtered out of the blood. The tubule of the nephron collects these substances. Some of the water is reabsorbed. The remaining fluid is urine.
  6. The kidneys maintain homeostasis by controlling the amount of water and dissolved substances in the blood. They do this by excreting more or less of the water or substances in urine. The kidneys also secrete hormones that control body processes and help maintain homeostasis. For example, one of the kidney hormones stimulates bone marrow to produce red blood cells when more are needed.

Day 39

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. The nervous system is a complex network of nervous tissue that carries electrical messages throughout the body.
  2. Answers may vary. Sample answer: Three functions of the nervous system are controlling muscles, maintaining balance, and sensing the internal and external environments.
  3. Neurons are nerve cells. They have a special shape that lets them pass electrical signals from one cell to another. Each neuron has three main parts: cell body, dendrites, and axon. The cell body contains the nucleus and other organelles. Dendrites receive nerve impulses from other cells. The axon passes on the nerve impulses to other cells. It branches at the end into multiple nerve endings so it can transmit impulses to many other cells. Nerve impulses are messages carried by
    neurons. Each nerve impulse is an electrical signal that is received by a dendrite, passed through the cell body and axon, and then passed on to another cell or cells.
  4. Answers may vary. Sample answer: Two nervous system diseases are meningitis and epilepsy.
    Meningitis is an infection of the membranes covering the brain and spinal cord. It is caused by bacteria or viruses. Symptoms of meningitis include headache, fever, and a stiff neck. Epilepsy is a disease in which seizures occur. A seizure is a period of lost consciousness that may include violent muscle contractions. It occurs because of abnormal electrical activity in the brain.
    Epilepsy may be caused by an infection, injury, or tumor. In many cases, however, the cause can’t be identified.
  5. A brain injury that affects a patient’s ability to see most likely injured the occipital lobe of the cerebrum. This part of the brain controls the sense of sight. It processes and interprets sensory information from the eyes.
  6. The nerve endings of an axon don’t actually touch the dendrites of other neurons. The messages must cross tiny gaps between neurons, called synapses. Chemicals called neurotransmitters carry the message across the gaps. When a nerve impulse arrives at the end of an axon, neurotransmitters are released. They travel across the synapse to the dendrite of another neuron.
    The neurotransmitters bind to the membrane of the dendrite. This triggers a nerve impulse in the next neuron.
  7. The nervous system has two main parts, called the central nervous system and the peripheral nervous system. The central nervous system includes the brain and spinal cord. The peripheral nervous system includes all of the rest of the nervous tissue in the body. It consists of a complex network of nerves that control all body parts. The brain in the central nervous system is the control center of the body. Nerve impulses pass back and forth between the brain and the peripheral nervous system via the spinal cord. Information from the peripheral nervous system is
    interpreted by the brain, which tells the peripheral nervous system how to make the body respond.

Day 46

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. Light passes through the cornea, through the pupil, through the lens; the lens focuses light on the retina , which has light-sensing photoreceptor cells called rods and cones. When light hits rods and cones, it causes chemical changes which start nerve impulses. The nerve impulses travel through the optic nerve to the brain which makes sense of the nerve impulses and tells you what you are seeing.
  2. The cornea is a clear, protective covering on the outside of the eye.
  3. The lens helps focus light at the back of the eye The lens must bend light from nearby objects more than it bends light from far-away objects. The lens changes shape to bend the light by just the right amount to bring objects into focus.
  4. Rods let us see in dim light. Cones let us detect light of different colors.

Day 48

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. Sample answer: Five human senses are vision, hearing, touch, taste, and smell.
  2. Light from an object enters the eye through the cornea and pupil and passes through the lens. Along with the cornea, the lens focuses the light to form an image on the retina at the back of the eye. This stimulates light-sensing cells in the retina to send nerve impulses to the optic nerve, which carries the impulses to the brain.
  3. Sound waves enter the outer ear and strike the eardrum, which vibrates. The vibrations are passed on to three tiny bones in the middle ear. These bones, called ossicles, amplify the vibrations. The vibrations next pass to the cochlea in the inner ear. The vibrations cause waves in the liquid inside the cochlea. The waves bend tiny hair cells that line the cochlea. These cells send nerve impulses to the auditory nerve, which carries the impulses to the brain.
  4. Food tastes bland when your nose is stuffy because your sense of smell is not working well. Without the smell of food, you are able to distinguish only five basic tastes.
  5. Human beings have 3-D vision because our two eyes face the same direction but are a few inches apart.
    This allows the eyes to focus on the same object at the same time but from slightly different angles. The brain uses the slightly different images from the two eyes to determine the distance to the object.
  6. Both taste and smell are senses that detect chemicals. Taste neurons are on the tongue and sense chemicals in food. They can detect only five different tastes. Smell neurons are in the nose and sense chemicals in the air. They can detect thousands of different odors.

Day 56

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. The two main roles of the male reproductive system are producing sperm, which are male gametes, and secreting testosterone, which is the major male sex hormone.

Day 57

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
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  1. Three functions of the female reproductive system are producing eggs, secreting estrogen, and supporting and giving birth to a baby.

Day 60

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. Light microscope
  2. All organisms are composed of cells; Cells are alive and the basic living units of organization in all organisms; All cells come from other cells.
  3. Cell, tissue, organ, organ system
  4. Transmission electron microscope
  5. No, cells can only come from other cells.

Day 61

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. prokaryotic and eukaryotic
  2. Organelles are compartments within a cell where specilized functions occur.
  3. Prokaryotic cells are much smaller and simpler than eukaryotic cells; eukaryotic cells can be considered to be “specialized” and contain membrane-bound organelles. Prokaryotic cells are surrounded by a cell wall. In prokaryotic cells the DNA forms a single large circle that coils up on itself. Eukaryotic cells have a nucleus with numerous chromosomes.
  4. The plasma membrane is a double layer of phospholipids lipids along with many special proteins. The function of the plasma membrane is to control what goes in and out of the cell. The plasma membrane gives the cell an inside that is separate from the outside world.
  5. The mitochondria is known as the powerhouse because it creates ATP which is used as energy for cell functions.
  6. As animal cells lack chloroplasts, the organelle in which photosynthesis occurs, this process cannot occur in animal cells.

Day 62

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. The cell membrane consists of two phospholipid layers. The interior of the membrane (lipid tails) is hydrophobic, or “water fearing.” The exterior of the membrane (lipid heads) is hydrophilic, or “water loving.” Proteins are also embedded in the lipid layers.
  2. Diffusion is the natural movement of a substance down the concentration gradient from an area of higher concentration to an area of lower concentration.
  3. Simple diffusion occurs when a small molecule moves through a cell membrane from an area of higher to lower concentration without help from transport proteins. The molecule simply squeezes between phospholipid molecules in the membrane. An example of simple diffusion is the diffusion of oxygen out of the lungs and into the blood.
  4. Osmosis is the special case of the diffusion of water.
  5. Passive transport of the substance will occur out of the cell because the concentration of the substance is greater inside than outside the cell. Transport out of the cell will occur naturally by diffusion down the concentration gradient, and this requires no energy.
  6. Passive and active transport are the two basic ways that substances may pass through cell membranes. Passive transport does not require energy. It occurs when a substance diffuses across a cell membrane from an area of higher to lower concentration. It may or may not need to be facilitated by transport proteins. Active transport requires energy. It occurs when a substance crosses a cell membrane from an area of lower to higher concentration or when the molecules of the substance are very large. Active transport up the concentration gradient is by a protein pump, such as the sodium-potassium pump. Active transport of very large molecules is by vesicles.
  7. Channel proteins form tiny holes called pores in the cell membrane. This allows water or hydrophilic molecules to cross the cell membrane without coming into contact with the hydrophobic interior of the membrane. Carrier proteins bind with diffusing molecules. This causes the proteins to change shape and carry the diffusing molecules across the membrane.

Day 63

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. Cellular respiration is the process in which cells break down glucose, release the stored energy, and use it to make ATP. Cellular respiration begins in the cytoplasm of cells. It is completed in mitochondria.
  2. The three stages of cellular respiration are glycolysis, the Krebs cycle, and electron transport.
    Two molecules of ATP are produced in glycolysis, and two more are produced in the Krebs cycle.
    Up to 34 molecules of ATP are produced in the electron transport stage.
  3. Fermentation is a process in which some organisms produce ATP from glucose without oxygen.  In other words, fermentation is an anaerobic process. There are two types of fermentation: lactic acid fermentation and alcoholic fermentation.
  4. Sample answer: I think that bacteria that live in the human intestines use anaerobic respiration to obtain ATP from glucose. That’s because there is little or no oxygen in the human intestines, and anaerobic respiration does not require oxygen.
  5. Cellular respiration and photosynthesis are closely related. They are like two sides of the same coin. The products of photosynthesis are needed for cellular respiration, and the products of cellular respiration are needed for photosynthesis. Together, the two processes store and release energy in virtually all living things.
  6. Both aerobic and anaerobic respiration release energy from glucose and use it to make ATP.   Aerobic respiration requires oxygen. Anaerobic respiration does not require oxygen. Aerobic respiration produces more molecules of ATP than anaerobic respiration does. However, anaerobic respiration occurs more quickly than aerobic respiration. It also allows organisms to live in places where there is little or no oxygen, such as deep under water or soil or inside other living things.

Day 64

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. DNA replication is the process in which DNA is copied. It occurs before a cell divides. It must occur so that each daughter cell will have a complete copy of the parent cell’s genetic material.
  2. Chromosomes are structures formed of DNA and protein molecules that are coiled into a definite shape. Chromosomes form from a cell’s DNA when the cell prepares to divide.
  3. In a prokaryotic cell, the steps of cell division are DNA replication, when the cell’s chromosome is copied; chromosome segregation, when the two copies of the chromosome move to opposite poles of the cell; and cytokinesis, when the cytoplasm splits apart and the cell pinches in two to form new daughter cells.
  4. The phases of mitosis are prophase, metaphase, anaphase, and telophase. In prophase, chromosomes form, the nuclear membrane breaks down, centrioles move to opposite poles, and spindles start to form. In metaphase, spindle fibers attach to the centromeres of sister chromatids, and sister chromatids line up at the center ofthe cell. In anaphase, spindle fibers shorten and pull the sister chromatids to opposite poles. In telophase, chromosomes uncoil, spindle fibers break down, and new nuclear membranes form.
  5. The single-celled organism belongs to the Eukarya domain so it has a nucleus. When the organism divides, DNA replication will be followed by the four phases of mitosis, in which the nucleus and chromosomes divide. Then the rest of the cell will divide by cytokinesis.
  6. Cell division is more complicated in eukaryotic than prokaryotic cells because eukaryotic cells have multiple chromosomes, a nucleus, and other organelles. When eukaryotic cells divide, the nucleus and other organelles must be copied and divided so that each daughter cell will end up with all the needed structures. The multiple chromosomes also must be separated in mitosis so that each daughter cell will have copies of all the chromosomes.
  7. A prokaryotic cell has a simpler cell cycle than a eukaryotic cell. A prokaryotic cell grows in size, replicates its DNA, and then divides, typically by binary fission. A eukaryotic cell goes through two main stages in its lifetime: interphase and mitotic phase. Interphase is longer than mitotic phase and divided into growth phase 1, synthesis, and growth phase 2. Mitotic phase consists of mitosis and cytokinesis.

Day 66

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. Gregor Mendel was an Austrian monk who lived during the 1800s. He did many experiments with pea plants. From his experiments, he discovered how parents pass traits to their offspring.
  2. Peas were a good choice of plants for Mendel to study for several reasons. They are easy to grow, and they grow quickly. They also have many traits that are easy to observe, and each trait exists in two different forms.
  3. Mendel’s law of segregation states that the two factors an individual inherits for a trait separate and go to different gametes when the individual reproduces. Mendel’s law of independent assortment states that factors controlling different traits go to gametes independently of each other.
  4. Plants that reproduce asexually produce offspring that are genetically identical to each other and to the parent. If Mendel had chosen to study these plants instead of peas, there would not have been any variation in traits between or within generations. Therefore, Mendel would not have been able to arrive at his laws of inheritance.
  5. Mendel needed to grow two offspring generations to develop his law of segregation because the first generation offspring had just one form of each trait. The reason is that one of the two factors controlling each trait was dominant to the other factor. Only by having this first generation produce offspring could Mendel determine that the two factors separated and went to different gametes. The second generation showed both forms of the trait due to segregation.
  6. Mendel’s second set of experiments showed that two different traits were inherited by the offspring independently of each other. The second generation of offspring had all possible combinations of the two traits. Mendel inferred from these results that the factors controlling different traits assorted independently in the formation of gametes.

Day 68

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. Genome refers to all the genetic information of a species. For example, the human genome is all the DNA of a human being.
  2. The Human Genome Project was an international effort to sequence all 3 billion bases in human DNA. By 2003, it had accomplished this goal. It also identified the more than 20,000 human genes and their locations on chromosomes.
  3. Answers may vary. Sample answer: An example of an autosomal recessive genetic disorder is cystic fibrosis. The recessive allele codes for a defective protein involved in mucus production.  People with two copies of the recessive allele have the disorder. They have unusually thick mucus that clogs airways in lungs and ducts in other organs.
  4. The disorder is an X-linked recessive disorder.
  5. Both the polymerase chain reaction and gene cloning are biotechnology methods that make many copies of a gene. The polymerase chain reaction uses high temperatures and an enzyme to make new DNA molecules. The process keeps cycling to make many copies of the gene. Gene cloning inserts the gene into bacteria. The bacteria divide rapidly, making many copies of the gene.
  6. Answers may vary. Sample answer: Pros of producing and using genetically modified organisms include more and better food crops and less use of pesticides. Cons include possible health or environmental problems caused by the use of GMOs. For example, plants genetically modified to produce pesticides might kill good as well as bad insects. Genes might also “escape” from the modified plants into wild plants through cross-pollination. This could negatively affect other species in the environment. One way of weighing the pros and cons is to think about how many species are likely to benefit or be harmed by the use of GMOs. Only human beings are likely to benefit from their use, whereas many species might be harmed.

Day 69

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. Bacteria are the most numerous living things on Earth. Their total number is estimated to be about 5 million trillion trillion.
  2. Two ways of classifying bacteria are by the shape of their cells and by the way they respond to Gram stain. There are three types of bacteria based on shape: bacilli, which are rod shaped; cocci, which are sphere shaped, and spirilli, which are spiral shaped. There are two types of bacteria based on Gram staining: gram-positive bacteria, which stain purple; and gram-negative bacteria, which stain red.
  3. Many bacteria benefit ecosystems by decomposing wastes and recycling carbon and nitrogen. Bacteria called cyanobacteria make food by photosynthesis and release oxygen to the atmosphere.
  4. Some uses of bacteria to people include helping us digest food and making vitamins inside the human digestive tract. People also use bacteria to create medical products, such as vaccines; transfer genes in gene therapy; make fuels such as ethanol; clean up oil spills; kill plant pests; and ferment foods.
  5. Lyme disease is caused by a bacterial pathogen. Ticks are the vectors that spread the disease from wild animals to people when they bite them.
  6. Cyanobacteria are photosynthetic bacteria. When they first appeared on early Earth, the atmosphere contained almost no oxygen. Oxygen is a waste product of photosynthesis. After cyanobacteria evolved, they started adding oxygen to the atmosphere. Many organisms that had evolved in the absence of oxygen were poisoned by it. These organisms died out. Other organisms not only survived but were able to evolve a new way of using the oxygen to extract energy from food. This was the process of cellular respiration. These organisms were more efficient and successful. They went on to become the most numerous types of organisms on
    Earth.
  7. Bacteria evolve resistance to antibiotic drugs through the process of natural selection. When an antibiotic is given to a sick patient, bacterial cells that are susceptible to the antibiotic die. If any of the bacterial cells are resistant to the antibiotic, they don’t die. Instead, they survive and reproduce. This leads to a population of bacteria that are resistant to the antibiotic drug.

Day 70

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. Archaeans are prokaryotes in the Archaea Domain.
  2. An extremophile is an organism that lives in extreme conditions.
  3. Four types of archaean extremophiles are halophiles, which can survive in very salty water; hyperthermophiles, which can survive at very high temperatures; acidophiles, which can survive in very acidic environments; and alkaliphiles, which can survive in very alkaline, or basic, environments.
  4. The cause of your symptoms is likely to be a bacterium. Bacteria cause many human diseases, including food poisoning. Archaeans, in contrast, are not known to cause any human diseases.
  5. Methanogens live inside the gut of animals like cows. They benefit the cows by helping them digest tough plant fibers made of cellulose.

Day 71

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. An infectious disease is a disease that is contagious because it is caused by a pathogen.
  2. Four types of human pathogens are bacteria, viruses, fungi, and protozoa. Examples may vary. Sample answer: An example of a disease caused by bacteria is tuberculosis. The common cold is caused by viruses. Athlete’s foot is a fungal disease. Malaria is caused by protozoa.
  3. A vector is an organism that spreads pathogens from one person or animal to another. Human diseases spread by vectors include Lyme disease and malaria.
  4. Posters may vary but should show ways that young children can reduce their risk of catching a cold, such as washing their hands often and thoroughly; not touching their eyes, nose, or mouth; and not sharing eating utensils or cups.
  5. Sample answer: If people with flu viruses on their hands touch a doorknob, some of the viruses might end up on the surface of the doorknob. When you touch the doorknob, you could pick up the viruses on your hand. Then, if you rub your nose or eyes with your hand, you might transfer viruses that could make you sick with the flu.

Day 72

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. A noninfectious disease is a disease that isn’t contagious because it isn’t caused by pathogens.
  2. A carcinogen is anything in the environment that causes cancer. Two examples of carcinogens are nicotine in tobacco and UV radiation in sunlight.
  3. Multiple sclerosis is caused by the immune system attacking the body’s nerve cells, which causes progressive weakness and pain.
  4. The single best way to reduce your risk of developing lung cancer is to avoid smoke and smoking.
  5. Sample answer: An example of an allergen that might trigger seasonal allergic responses is plant pollen. An example of an allergen that might trigger year-round allergic responses is dust mites.
  6. Mutations that can lead to cancer usually occur in genes that control the cell cycle. Because of the mutations, abnormal cells are allowed to divide. The cells divide out of control and may form a tumor.
  7. Type 1 diabetes is caused by the immune system attacking and destroying insulin-producing cells of the pancreas. As a result, the cells can no longer produce insulin. This type of diabetes usually develops in childhood or adolescence. Type 2 diabetes is much more common than type 1 diabetes. Type 2 diabetes occurs when body cells no longer respond normally to insulin. The pancreas still makes insulin, but the cells of the body can’t use it. Being overweight and having high blood pressure increase the chances of developing type 2 diabetes. This type of diabetes usually develops in adulthood.

Day 73

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. The skin forms a physical barrier between the body and the outside environment that keeps out most pathogens. The outer layer of the skin forms a tough, waterproof covering that is very difficult for pathogens to penetrate.
  2. Fluids released by your body—including mucus, tears, saliva, and sweat—contain enzymes called lysozymes. These chemicals break down the cell walls of bacteria and kill them. Hydrochloric acid in the stomach is another chemical barrier. It kills most pathogens that enter the stomach in food or water. Urine is also acidic, so few pathogens are able to grow in it, providing a chemical barrier in the urinary system.
  3. Phagocytosis is the process in which white blood cells called phagocytes engulf and destroy pathogens and dead cells. It occurs when damage to tissue results in the release of chemicals that attract white blood cells to the area of damage. The white blood cells leak out of blood vessels and into the damaged tissue, where they start “eating” pathogens and dead cells.
  4. Redness, warmth, and pain are indications of inflammation. Inflammation occurs when tissue has been damaged and pathogens have entered the body. Therefore, they indicate that the scrape has become infected.
  5. A fever is a higher-than-normal body temperature. Many pathogens cannot multiply as rapidly when the body’s temperature is higher than normal, so a fever helps keep an infection in check. A fever also causes the immune system to make more white blood cells to fight the infection.

Day 74

(Answers from CK-12 Life Science For Middle School Teacher’s Edition
http://www.ck12.org/saythanks)

  1. An immune response is the immune system’s reaction to a specific pathogen.
  2. Sample answer: Three immune system organs are bone marrow, the thymus gland, and the spleen. Bone marrow produces lymphocytes, which are the white blood cells involved in an immune response. The thymus gland stores lymphocytes called T cells while they mature. The spleen filters pathogens from the blood.
  3. A patient who tests positive for antibodies to the antigens of a particular pathogen must have been infected with that pathogen at some point in time.
  4. B cells respond to pathogens in the blood and lymph by making antibodies. Antibodies bind with antigens on pathogens, thus signaling their destruction by phagocytosis. T cells respond to infected, damaged, or cancerous cells by producing toxins. The toxins make tiny holes in the cell membranes, causing the cells to burst and die, along with any pathogens they contain.
  5. Vaccinations deliberately expose you to pathogens so you will develop immunity to them. The pathogens are usually injected under the skin, but only part of the pathogens are injected, or else weakened or dead pathogens are used. This is enough to cause an immune response without causing the disease. If you are ever exposed to the actual pathogens in the future, your immune system will be able to kill them before they can make you sick.

Day 82-83

1. Unicellular
2. Nerve
3. Digestive
4. Organism
5. Multicellular
6. System
7. Muscle
8. Organ
9. Excretory
10. Tissue
11. Food
12. Muscular
13. Connective
14. Cells
15. Ho9meostatis
16. Epithelial
17. Skeletal
18. Respiratory
19. Reproductive
20. Integumentary
21. Endocrine
22. Circulatory
23. Immune