GED Life Science Practice

Life science is the largest single slice of the GED Science test at roughly 40 percent. These questions cover the specific subtopics the exam returns to again and again.

Question 1 of 27

0 answered

Oxpecker birds ride on zebras and eat the ticks living on their skin. The birds get a steady food supply, and the zebras lose blood-sucking parasites. Which term best describes the relationship between oxpeckers and zebras?

Life science study guide

Life science is one of the two largest areas of the GED Science test. It covers living things from the cell up to whole ecosystems. The test usually supplies a passage, diagram, or data set, so you need the core ideas well enough to read that material quickly and correctly.

Cells and their parts

All living things are made of cells, and every cell comes from an existing cell. Prokaryotic cells, such as bacteria, have no nucleus. Eukaryotic cells, such as plant and animal cells, keep their DNA inside a nucleus and have specialized organelles.

Know a few organelles by job rather than by drawing. The nucleus holds genetic instructions. Mitochondria release energy from food through cellular respiration. Ribosomes build proteins. The cell membrane controls what enters and leaves. Plant cells also have a cell wall for support and chloroplasts for photosynthesis.

Photosynthesis and cellular respiration

These two processes run in opposite directions. Photosynthesis uses light energy, carbon dioxide, and water to make glucose and release oxygen. Cellular respiration uses glucose and oxygen to release energy, producing carbon dioxide and water.

A common question type gives a graph of plant growth or oxygen output under different light levels and asks what the data shows. Identify the variable the experimenter changed and what was measured before you read the answer choices.

Genetics and heredity

Genes are segments of DNA that carry instructions for traits. Each parent passes on one copy of each gene, called an allele. A dominant allele shows its trait whenever it is present. A recessive allele shows its trait only when both copies are recessive.

A Punnett square predicts the possible offspring of two parents. Put one parent’s alleles across the top and the other’s down the side, then fill in each box. The boxes give probabilities, not guarantees for any single child.

Worked example

Brown eyes (B) are dominant over blue eyes (b). Two parents are both Bb. What is the chance a child has blue eyes?

  1. Cross Bb × Bb. The four boxes are BB, Bb, Bb, and bb.
  2. Only bb shows the recessive blue trait.
  3. One box out of four: a 25 percent chance.

Evolution and natural selection

Individuals in a population vary, partly because of mutations. When some variations help an organism survive and reproduce in its environment, those organisms leave more offspring, and the helpful traits become more common over generations. That process is natural selection.

Separate inherited traits from acquired ones. A bodybuilder’s muscles are acquired and are not passed to children. Only changes in the genes of reproductive cells can be inherited. Populations evolve; individual organisms do not.

Human body systems and health

The test treats the body as connected systems. The circulatory system moves blood, oxygen, and nutrients. The respiratory system exchanges oxygen and carbon dioxide. The digestive system breaks food into nutrients. The nervous and endocrine systems send signals that keep conditions inside the body stable, a balance called homeostasis.

Health questions often involve disease. Bacteria are living cells and can be treated with antibiotics. Viruses are not cells and are not affected by antibiotics. Vaccines train the immune system to recognize a pathogen before a real infection.

Ecosystems and energy flow

Energy enters most ecosystems through producers, such as plants, which capture sunlight. Primary consumers eat producers, secondary consumers eat primary consumers, and decomposers break down dead matter. Only about 10 percent of the energy at one level reaches the next, which is why food chains are short and top predators are few.

Expect questions that remove or add a species and ask what happens next. Follow the arrows in the food web: if a predator disappears, its prey usually increases at first, and then whatever the prey eats tends to decrease.

Population growth and limiting factors

A population is all the members of one species living in one area. Its size changes for only four reasons: births and immigration add individuals, while deaths and emigration remove them. When births plus arrivals are greater than deaths plus departures, the population grows. When the reverse is true, it shrinks.

With plenty of food and space and few predators, a population can grow faster and faster, often doubling in a set amount of time. This is exponential growth, and it shows as a curve that bends sharply upward. It never lasts. Sooner or later something runs short, such as food, water, nesting space, or oxygen. A resource or condition that holds a population back is called a limiting factor.

Over time, many populations level off near the largest size their environment can support, called the carrying capacity. On a graph, the count rises quickly and then flattens out. If a population overshoots, for example after its predators are removed, it can use up its food and then crash.

Some limiting factors grow stronger as a population gets crowded. Contagious disease, competition for food, and stress all hit harder when animals live close together. Others, such as floods, fires, and hard frosts, strike about the same way no matter how many animals there are. When two species need the same limited resource, they compete, and one may push the other out of an area completely.

Worked example

A pond has 2,000 frogs at the start of a year. During the year, 600 frogs hatch, 750 die, 50 move in from a nearby stream, and none leave. What is the population at the end of the year, and is it growing or shrinking?

  1. Add what joins the population: 600 births + 50 arrivals = 650.
  2. Add what leaves it: 750 deaths + 0 departures = 750.
  3. Find the net change: 650 − 750 = −100.
  4. Apply it to the starting count: 2,000 − 100 = 1,900 frogs, so the population is shrinking.

Checklist before test day

You should be able to explain each of these in one sentence.

  • What the nucleus, mitochondria, and chloroplasts do.
  • How photosynthesis and respiration are reverses of each other.
  • How to fill in a Punnett square and read a probability from it.
  • Why acquired traits are not inherited.
  • Why antibiotics do not work on viruses.
  • How removing one species changes a food web.

Life Science practice set 1: 27 questions with answers

Work each question on paper first, then open the answer to check your reasoning.

  1. 1.Oxpecker birds ride on zebras and eat the ticks living on their skin. The birds get a steady food supply, and the zebras lose blood-sucking parasites. Which term best describes the relationship between oxpeckers and zebras?

    1. A.Mutualism, because both species benefit
    2. B.Competition, because both need the same food
    3. C.Commensalism, because only one benefits
    4. D.Parasitism, because one species is harmed
    Show answer

    Answer: A. Mutualism, because both species benefit

    Both the birds (food) and the zebras (fewer parasites) gain something, which defines mutualism. The ticks are parasites of the zebra, but the oxpecker itself is not harming the zebra.

  1. 2.A forest ecologist measures carbon dioxide (CO₂) in the air under the tree canopy over several days. CO₂ is lowest in the late afternoon and highest just before dawn. Which explanation best fits this pattern?

    1. A.Photosynthesis removes CO₂ by day, and respiration adds it at night
    2. B.Plants carry out respiration only during the daylight hours
    3. C.Decomposers in the soil are active only in the late afternoon hours
    4. D.Photosynthesis adds CO₂ by day and stops completely at night
    Show answer

    Answer: A. Photosynthesis removes CO₂ by day, and respiration adds it at night

    In daylight, photosynthesis pulls CO₂ out of the air faster than respiration adds it; at night only respiration continues, so CO₂ builds up until dawn. Plants respire around the clock, not only in daylight.

  1. 3.A bag of garden fertilizer explains that it supplies nitrogen, which plants need to build proteins. In a plant cell, which structures put proteins together?

    1. A.Cell walls
    2. B.Ribosomes
    3. C.Vacuoles
    4. D.Chloroplasts
    Show answer

    Answer: B. Ribosomes

    Ribosomes assemble proteins from amino acids using instructions from DNA. Chloroplasts are a tempting choice for plants, but they carry out photosynthesis, not protein building.

  1. 4.A fitness class recorded the average heart rate of five adults. At rest: 72 beats per minute After 10 minutes of stair climbing: 128 beats per minute After 5 minutes of rest: 90 beats per minute Which statement is supported by the data?

    1. A.Heart rate stayed about the same during both exercise and rest periods
    2. B.Heart rate rose with exercise and was heading back toward resting levels
    3. C.Heart rate returned fully to 72 beats per minute after 5 minutes of rest
    4. D.Heart rate fell during exercise and then rose again during the rest period
    Show answer

    Answer: B. Heart rate rose with exercise and was heading back toward resting levels

    The rate climbed from 72 to 128 during exercise and fell to 90 after rest, which is moving back toward 72. It had not fully returned, since 90 is still above the resting rate.

  1. 5.Sickle cell disease is caused by a change in a single DNA base. The change places a different amino acid in the hemoglobin protein, and red blood cells become stiff and sickle-shaped. What does this example best show?

    1. A.The shape of a cell has no connection to its genetic code
    2. B.Every change in DNA makes an organism more likely to survive
    3. C.Proteins in the body are built directly from stored lipids
    4. D.A change in DNA can alter a protein and the trait it produces
    Show answer

    Answer: D. A change in DNA can alter a protein and the trait it produces

    The passage traces a path from a DNA change to a protein change to a visible trait. The example shows a harmful mutation, so it contradicts the claim that every DNA change helps survival.

  1. 6.Wildlife staff counted deer on a fenced nature reserve every other year. Year 1: 40 Year 3: 110 Year 5: 180 Year 7: 195 Year 9: 190 Which statement best describes the population from Year 7 to Year 9?

    1. A.It is about to die out because the numbers are falling fast
    2. B.It is growing faster than at any earlier point in the study
    3. C.It has leveled off near the carrying capacity of the reserve
    4. D.It doubled every two years, just as it did at the start
    Show answer

    Answer: C. It has leveled off near the carrying capacity of the reserve

    Growth slowed and the count held near 190 to 195, which is what happens when a population reaches the limit its habitat can support. A drop from 195 to 190 is small, so it does not show the population dying out.

  1. 7.A lab technician examines a sample under a microscope. The organism is made of one cell, has no nucleus, and reproduces by splitting in two. The organism is most likely

    1. A.a fern
    2. B.a bacterium
    3. C.an insect
    4. D.a mushroom
    Show answer

    Answer: B. a bacterium

    Single-celled organisms without a nucleus are prokaryotes, such as bacteria. Mushrooms are fungi, which are eukaryotes with nuclei in their cells.

  1. 8.Saliva contains an enzyme that starts breaking down starch in the mouth. Other enzymes in the stomach and small intestine continue the process. What is the main purpose of digestion?

    1. A.To remove carbon dioxide made by the body’s working muscles
    2. B.To break large food molecules into small ones the body can absorb
    3. C.To move oxygen from the lungs into the bloodstream for cells
    4. D.To join small food molecules into large ones for later storage
    Show answer

    Answer: B. To break large food molecules into small ones the body can absorb

    Digestive enzymes split large molecules like starch into small ones such as glucose that can pass into the blood. Building large molecules for storage happens later in cells, not during digestion.

  1. 9.Researchers counted bird species in 10 city parks. Parks with more native trees had more bird species. The parks also differed a great deal in total size. Why can the researchers not conclude that native trees alone caused the higher number of bird species?

    1. A.Ten parks is too many to compare in a single research study
    2. B.Native trees provide no food or shelter for any kind of bird
    3. C.Birds cannot be counted with any accuracy in a city setting
    4. D.Park size could also explain the difference in bird species
    Show answer

    Answer: D. Park size could also explain the difference in bird species

    Because park size also varied, larger parks might have more birds and more trees, so size is a possible alternate cause. Ten parks is a small sample, not too many.

  1. 10.Strawberry plants send out long stems called runners. Where a runner touches soil, it grows roots and becomes a new plant that is genetically identical to the parent. This is an example of

    1. A.asexual reproduction, which makes offspring identical to the parent
    2. B.fertilization, which joins an egg cell together with a sperm cell
    3. C.sexual reproduction, which mixes the genes of two separate parents
    4. D.pollination, which carries pollen from one flower to another flower
    Show answer

    Answer: A. asexual reproduction, which makes offspring identical to the parent

    Only one parent is involved and the offspring are identical copies, which defines asexual reproduction. Sexual reproduction would produce offspring with a mix of two parents’ genes.

  1. 11.A cook touches a hot pan and pulls the hand away before even feeling pain. This automatic response is called a reflex. Which body system controls this response?

    1. A.Excretory system
    2. B.Skeletal system
    3. C.Nervous system
    4. D.Digestive system
    Show answer

    Answer: C. Nervous system

    Nerves carry the signal from the skin to the spinal cord and back to the arm muscles, which is the work of the nervous system. Bones of the skeletal system move only when muscles are signaled by nerves.

  1. 12.Some whale species have small hip bones buried in their bodies. These bones are not attached to any legs and do not help the whale swim. What do these bones best support?

    1. A.Whales will grow back legs in future generations
    2. B.The hip bones help whales swim faster than most fish
    3. C.Whales descended from ancestors that had back legs
    4. D.Whales and fish share the same hip bone structure
    Show answer

    Answer: C. Whales descended from ancestors that had back legs

    Leftover structures with no current use are evidence that an ancestor used them, in this case for legs. Evolution does not aim at a future goal, so the claim that whales will regrow legs is not supported.

  1. 13.A river slowly changes course and splits a squirrel population into two groups that cannot cross. Thousands of years later, squirrels from the two sides look different and can no longer interbreed. This outcome is best described as

    1. A.asexual reproduction that keeps both groups the same
    2. B.mutualism between two groups that help each other survive and grow
    3. C.the formation of new species after the groups were separated
    4. D.ecological succession that follows a sudden disturbance
    Show answer

    Answer: C. the formation of new species after the groups were separated

    Separated groups that change until they can no longer interbreed have formed new species. Succession describes changes in a whole community after a disturbance, not one population splitting into two species.

  1. 14.A biology instructor lists the conditions needed for natural selection to change a population. Which condition must be present?

    1. A.Food and space are unlimited for all individuals
    2. B.Individuals differ in traits that can be inherited
    3. C.Every individual in the group has exactly identical genes
    4. D.Organisms change their genes when they need to
    Show answer

    Answer: B. Individuals differ in traits that can be inherited

    Selection works only when inherited differences exist for the environment to favor. If every individual had identical genes, no trait could become more common than another.

  1. 15.A forestry worker reads that a large tree stores tons of carbon in its wood. Where does most of the carbon in a tree’s wood come from?

    1. A.Water pulled up from the soil through the roots
    2. B.Sunlight captured by the leaves
    3. C.Minerals absorbed from the soil
    4. D.Carbon dioxide taken in from the air
    Show answer

    Answer: D. Carbon dioxide taken in from the air

    During photosynthesis, a tree takes carbon dioxide from the air and builds its carbon atoms into sugars, which become wood. Soil minerals supply only small amounts of nutrients, not most of the tree’s mass.

  1. 16.A garden center poster describes how plants make their own food. Which list shows what a plant takes in to carry out photosynthesis?

    1. A.Glucose, water and stored chemical energy
    2. B.Carbon dioxide, oxygen and heat
    3. C.Oxygen, glucose and light energy
    4. D.Carbon dioxide, water and light energy
    Show answer

    Answer: D. Carbon dioxide, water and light energy

    Photosynthesis uses carbon dioxide, water and energy from light to make glucose. Oxygen and glucose are what photosynthesis produces, not what it takes in.

  1. 17.A trout population in a lake stops growing even though there is plenty of food. Tests show that the water holds very little dissolved oxygen during the summer. In this lake, the low oxygen level is acting as

    1. A.a producer that supplies energy to the food chain
    2. B.a predator that raises the death rate of the trout each year
    3. C.a limiting factor that caps the size of the population
    4. D.a partner species that helps the trout survive
    Show answer

    Answer: C. a limiting factor that caps the size of the population

    A resource in short supply that keeps a population from growing is a limiting factor. Oxygen is not a living thing, so it cannot be a producer or a predator.

  1. 18.Ranchers removed most of the coyotes from a valley. Jackrabbit numbers rose sharply for three years. Then, after the rabbits had eaten the grass down to bare ground, rabbit numbers dropped sharply. Which statement best explains the drop?

    1. A.The rabbits ran short of food after overgrazing
    2. B.Coyotes returned and ate most of the extra rabbits
    3. C.Rabbits stopped breeding once the coyotes were gone
    4. D.The grass grew too fast for the rabbits to eat it
    Show answer

    Answer: A. The rabbits ran short of food after overgrazing

    The passage links the drop to the grass being eaten bare, which means the rabbits outgrew their food supply. Nothing in the passage says the coyotes came back, so that choice is not supported.

  1. 19.Biologists count 240 snails in a 60-square-meter section of a salt marsh. What is the population density of snails in this section?

    1. A.40 snails per square meter
    2. B.0.25 snails per square meter
    3. C.180 snails per square meter
    4. D.4 snails per square meter
    Show answer

    Answer: D. 4 snails per square meter

    Density is the number of individuals divided by the area: 240 ÷ 60 = 4 snails per square meter. The answer 0.25 comes from dividing the area by the count, which is upside down.

  1. 20.A physical therapist explains that a muscle can only pull on a bone. It cannot push. How are muscles able to both bend and straighten the elbow?

    1. A.They work in pairs, as one contracts while the other relaxes
    2. B.The muscles stretch the bone so that the whole arm can grow longer
    3. C.One muscle pushes the bone forward and then pulls it back
    4. D.A single muscle contracts and relaxes at the very same time
    Show answer

    Answer: A. They work in pairs, as one contracts while the other relaxes

    Because muscles can only pull, a pair is needed: one muscle bends the joint and the opposite muscle straightens it. The first choice describes pushing, which the therapist says muscles cannot do.

  1. 21.When a person is suddenly frightened, glands above the kidneys release adrenaline into the blood. Within seconds, the heart beats faster and breathing speeds up. Which body system releases adrenaline?

    1. A.Immune system
    2. B.Endocrine system
    3. C.Digestive system
    4. D.Skeletal system
    Show answer

    Answer: B. Endocrine system

    The endocrine system is made of glands that release hormones, such as adrenaline, into the blood. The immune system fights infections and does not release this kind of signal.

  1. 22.A lab technician looks at cells under a microscope. Each cell has a stiff outer wall, a nucleus and many small green structures called chloroplasts. The sample most likely came from

    1. A.a frog’s muscle
    2. B.a soil bacterium
    3. C.a human cheek
    4. D.a spinach leaf
    Show answer

    Answer: D. a spinach leaf

    A cell wall together with chloroplasts marks a plant cell, such as one from a leaf. A bacterium may have a cell wall, but it has no nucleus and no chloroplasts.

  1. 23.A human body cell has 46 chromosomes. Egg and sperm cells form by meiosis, which halves the number of chromosomes. How many chromosomes does a human egg cell have?

    1. A.46
    2. B.23
    3. C.12
    4. D.92
    Show answer

    Answer: B. 23

    Meiosis halves the chromosome number, so 46 ÷ 2 = 23. The answer 46 is the number in body cells made by mitosis, not in egg cells.

  1. 24.A hiker caught in cold rain starts to shiver and cannot stop. How does shivering help the hiker’s body?

    1. A.Fast muscle movement releases heat to warm the body
    2. B.Shivering lets sweat escape so the skin cools down
    3. C.Shivering slows the heart so the body saves oxygen
    4. D.Shivering sends warm blood away from the body core
    Show answer

    Answer: A. Fast muscle movement releases heat to warm the body

    Shivering is a homeostasis response: quick muscle contractions release heat to raise body temperature. Sweating cools the body, which is the opposite of what a cold hiker needs.

  1. 25.Scientists measured the amount of a pesticide in a lake food chain. Water: 0.00005 ppm Tiny plankton: 0.04 ppm Small fish: 0.5 ppm Large fish: 2 ppm Fish-eating birds: 25 ppm Which pattern do the data show?

    1. A.The fish-eating birds produced the pesticide inside their bodies
    2. B.Most of the pesticide stayed dissolved in the lake water itself
    3. C.The pesticide grew more concentrated at each higher feeding level
    4. D.Each feeding level held about the same total amount of the pesticide
    Show answer

    Answer: C. The pesticide grew more concentrated at each higher feeding level

    The levels rise at every step from water to birds, so the pesticide builds up as it moves up the food chain. The water has the lowest level of all, which rules out the idea that it holds most of the pesticide.

  1. 26.After a bone marrow transplant, a patient’s new marrow begins making red blood cells, white blood cells and platelets. All of these come from one kind of cell in the marrow. What kind of cell is this?

    1. A.A stem cell that can specialize
    2. B.A nerve cell that sends signals
    3. C.A mature red blood cell
    4. D.A bacterium living in the bone
    Show answer

    Answer: A. A stem cell that can specialize

    Blood stem cells in the marrow can divide and develop into many specialized blood cell types. A mature red blood cell is already specialized and has no nucleus, so it cannot divide into other cell types.

  1. 27.A science article explains that if a cell grew very large, its surface area would not keep up with its volume. Why would a very large cell have trouble surviving?

    1. A.It would hold too much DNA for a single nucleus to store
    2. B.It would have too little cytoplasm to fill the space inside
    3. C.It would have too many mitochondria to fit inside its membrane
    4. D.Its membrane could not take in enough nutrients for the whole cell
    Show answer

    Answer: D. Its membrane could not take in enough nutrients for the whole cell

    Nutrients and wastes cross the cell membrane, and as a cell grows, its volume increases faster than its surface area, so the membrane cannot serve the whole cell. The DNA choice is tempting, but the limit described is about surface and volume, not genetic storage.

More practice sets

Life Science has 3 practice sets. None of these questions appear in the full practice tests.

Cells and energy on the GED Science test

Know what each major organelle does in one sentence: mitochondria release energy, ribosomes build proteins, the nucleus stores DNA, chloroplasts capture light. Then know the two energy processes as a pair. Photosynthesis takes in carbon dioxide and water and produces glucose and oxygen; cellular respiration does the reverse. Questions often set them side by side and ask what happens if one is disrupted.

Mitosis produces two identical cells for growth and repair. Meiosis produces sex cells with half the chromosome number. The GED rarely asks for the phases by name, but it does ask which process fits a described situation.

GED genetics and heredity questions

Punnett squares appear consistently. A cross of Tt with Tt gives one TT, two Tt, and one tt, so 75 percent show the dominant trait and 25 percent show the recessive one. Practice until you can draw and read the square in under thirty seconds.

Also expect questions about the difference between an inherited trait and an acquired one, and about how mutations introduce variation that natural selection can then act on.

Ecosystems and evolution on the GED

Food chain questions ask about energy flow: producers capture energy, consumers pass it along, decomposers return nutrients to the soil. Energy decreases at each level, which is why a pyramid diagram narrows toward the top.

Natural selection questions are usually written as short scenarios. The correct answer will describe a heritable trait improving survival and reproduction in a specific environment, not an organism choosing to change, and not the environment creating a new gene.

Frequently asked questions

What percentage of GED Science is life science?
About 40 percent of the Science test covers life science content.
Do I need to know the phases of mitosis by name?
Rarely. The test is more likely to ask what mitosis accomplishes and how it differs from meiosis.