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Science 8

Science 8 · Worksheets

Mixed review · Cells and water systems

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

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Mixed review · Cells and water systems

Science 8 · maddyhelps.com

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Circle the best answer for each question. Show your work in the space provided.

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

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

  3. 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) condensation
    3. c) filtration
    4. d) diffusion

  4. About 97% of Earth's water is salt water in the oceans. Where is most of the remaining fresh water?

    1. a) Underground, as groundwater
    2. b) In lakes, rivers, ponds and wetlands
    3. c) Frozen in ice caps and glaciers
    4. d) In the air, as water vapour

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

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

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

  7. You touch a hot pan and pull your hand away before you even feel the pain. How can the movement come before the feeling?

    1. a) Muscles in the hand sense the heat and pull away on their own
    2. b) The brain decides so quickly that you do not notice it deciding
    3. c) The spinal cord sends a signal straight back to the arm muscles
    4. d) The eyes spot the danger and send a signal straight to the arm

  8. A factory returns warm water to a river. Tests show 10 mg/L of dissolved oxygen upstream, at 12 °C, and 8 mg/L just downstream, at 24 °C. Which explanation fits best?

    1. a) Warm water can hold less dissolved oxygen than cold water
    2. b) The faster flow downstream carries the oxygen away
    3. c) Oxygen sinks in warm water, below where the tests were taken
    4. d) Warm water can hold more dissolved oxygen than cold water

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

  10. Happy Valley-Goose Bay, in Labrador, and Dublin, in Ireland, are both about 53° north of the equator, yet Goose Bay's winters are far colder. Which ocean currents help explain this?

    1. a) The same warm current flows past both, cooling on the way
    2. b) No currents; Ireland is simply closer to the equator
    3. c) A warm current reaches Ireland; a cold one flows past Labrador
    4. d) A cold current reaches Ireland; a warm one flows past Labrador

Answer key · Mixed review · Cells and water systems

Science 8 · maddyhelps.com

  1. c) 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.
  2. d) 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.
  3. d) 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.
  4. c) Frozen in ice caps and glaciers — Roughly two-thirds of Earth's fresh water is frozen, mostly in Antarctica and Greenland, and nearly all the rest is underground. Lakes and rivers, the fresh water we see and use most, hold only a tiny fraction of it.
  5. 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.
  6. a) 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.
  7. c) The spinal cord sends a signal straight back to the arm muscles — This is a reflex: the message from the nerves in your skin reaches the spinal cord, which sends a signal straight back to the muscles, so the hand moves before the brain has turned the message into a feeling of pain. Muscles cannot sense heat themselves; they move only when a nerve signal tells them to.
  8. a) Warm water can hold less dissolved oxygen than cold water — Gases dissolve better in cold water than in warm, the opposite of most solids, so warming a river drives some of its oxygen out. Fish and insects that need a lot of oxygen, such as trout and stonefly nymphs, suffer below the outlet; this is called thermal pollution.
  9. a) 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.
  10. c) A warm current reaches Ireland; a cold one flows past Labrador — The Gulf Stream and its extension, the North Atlantic Drift, carry warm water from the tropics across the Atlantic toward Ireland, while the cold Labrador Current flows south from the Arctic along Labrador's coast. Air over each coast takes on the warmth or chill of the water, so places at the same latitude can have very different winters.