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Cells and systems

Ten questions of mixed difficulty, covering Cells and systems. Print it, or work through it on screen — the answer key starts on its own page.

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Cells and systems

Science 8 · maddyhelps.com

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  1. Strips of fresh potato are left in very salty water for an hour. They come out limp and a little shorter. What happened?

    1. a) Water moved from the salty water into the potato cells
    2. b) Water moved out of the potato cells into the salty water
    3. c) The salt dissolved the walls of the potato cells
    4. d) Salt moved into the potato cells and made them shrink and collapse

  2. When a person's kidneys fail, a dialysis machine can do part of their job. Blood is pumped through the machine and back into the body. What must the machine do to the blood?

    1. a) Add oxygen and remove carbon dioxide
    2. b) Filter out wastes and extra water
    3. c) Pump it round the body in the heart's place
    4. d) Add nutrients from digested food

  3. The stomach is built from muscle tissue, nerve tissue, connective tissue and a lining that makes digestive juices. Together, these make the stomach

    1. a) a tissue
    2. b) a cell
    3. c) an organ system
    4. d) an organ

  4. An amoeba is a single cell. A grizzly bear is made of trillions of cells. Which statement about them is true?

    1. a) The amoeba's one cell does every job; the bear's cells specialize
    2. b) The amoeba needs no food, because one cell uses so little energy
    3. c) The amoeba is not really alive, because it is made of only one cell
    4. d) Each of the bear's cells can do every job the whole bear does

  5. A drop of food colouring is placed in a glass of still water. An hour later the colour has spread through the whole glass, with no stirring. This spreading is

    1. a) osmosis
    2. b) filtration
    3. c) diffusion
    4. d) condensation

  6. In the lungs, oxygen moves from the air sacs into the blood, while carbon dioxide moves from the blood into the air sacs. What decides which way each gas moves?

    1. a) Oxygen is lighter than carbon dioxide, so it rises into the blood
    2. b) Membranes let oxygen pass only inward and carbon dioxide only outward
    3. c) The lungs pump oxygen in and push carbon dioxide out of the blood
    4. d) Each moves from where it is more concentrated to where it is less

  7. At 40× magnification, a microscope's field of view is 4 mm across. At 400×, eight cheek cells fit across the field end to end. About how wide is one cheek cell?

    1. a) 0.05 mm
    2. b) 0.4 mm
    3. c) 5 mm
    4. d) 0.5 mm

  8. Under a microscope, a student sees box-shaped cells, each with a thick outer wall and many small green bodies inside. The sample most likely came from

    1. a) a drop of blood
    2. b) a leaf
    3. c) the inside of a cheek
    4. d) a frog's skin

  9. Which of these structures is found in both plant cells and animal cells?

    1. a) Chloroplasts
    2. b) Mitochondria
    3. c) A cell wall
    4. d) A large central vacuole

  10. Many vaccines contain a weakened or killed germ, or a harmless piece of one. How does a vaccine protect a person from the real disease?

    1. a) It makes the body's cells impossible for any germ to infect
    2. b) It trains the immune system to recognize and destroy the germ
    3. c) It coats the airways so the germ can never get into the body
    4. d) It kills any of the germ already in the body, as an antibiotic does

Answer key · Cells and systems

Science 8 · maddyhelps.com

  1. b) Water moved out of the potato cells into the salty water — In osmosis, water moves through a membrane from where there is more water, and less dissolved material, to where there is less water. The salty water outside has less water than the cell contents, so water leaves the cells and the strips go limp; in fresh water they would firm up instead.
  2. b) Filter out wastes and extra water — The kidneys are the main organs of the excretory system: they filter wastes such as urea, along with extra water, out of the blood to make urine. Adding oxygen and removing carbon dioxide is the lungs' job, in the respiratory system, which still works in a person on dialysis.
  3. d) an organ — A tissue is a group of similar cells doing one job, and an organ is several kinds of tissue working together. The stomach is one organ in the digestive system; the system is the whole team of organs, from the mouth to the intestines.
  4. a) The amoeba's one cell does every job; the bear's cells specialize — A single-celled organism must take in food, get rid of wastes, move and reproduce, all within one cell. In a multicellular organism, cells specialize as muscle, nerve, blood and other cells and depend on each other, so one bear cell could not survive on its own.
  5. c) diffusion — Diffusion is the spreading of particles from where they are more concentrated to where they are less, driven by their constant random motion. Osmosis is one kind of diffusion, the movement of water through a membrane, and there is no membrane here.
  6. d) Each moves from where it is more concentrated to where it is less — Blood arriving at the lungs is low in oxygen and high in carbon dioxide, so each gas diffuses from high concentration to low, and they go opposite ways at the same time. In the muscles the concentrations are reversed, so there oxygen leaves the blood and carbon dioxide enters: the membrane lets both gases through either way.
  7. a) 0.05 mm — Ten times the magnification shows a field ten times narrower, so at 400× the field is 4 ÷ 10 = 0.4 mm across, and each cell is 0.4 ÷ 8 = 0.05 mm, or 50 µm. Dividing the low-power field by 8 gives 0.5 mm, ten times too big, because it forgets that the field shrank.
  8. b) a leaf — A cell wall and green chloroplasts belong to plant cells, and leaf cells are packed with chloroplasts for photosynthesis. Animal cells, such as cheek, blood and skin cells, are bounded by a thin cell membrane and have no cell wall and no chloroplasts.
  9. b) Mitochondria — Every plant and animal cell needs energy, and mitochondria release it from food. It is easy to think plants can do without them because they have chloroplasts, but chloroplasts only make the food; a plant's mitochondria still have to release the energy stored in it.
  10. b) It trains the immune system to recognize and destroy the germ — The immune system learns to recognize the germ from the vaccine without the person falling ill, and remembers it, so if the real germ arrives it is destroyed before it can cause disease. A vaccine prevents an infection rather than curing one; killing bacteria already in the body is what antibiotics do.