1.1.1 Why animals need a circulation and the role of water Quiz: Pearson Edexcel Biology A (Salters-Nuffield), Unit 1

The 20 questions

1. Why do many large animals need a circulatory system instead of relying on diffusion alone?

   • Diffusion only works across membranes that are rich in blood, so a pump is needed first
   • Diffusion can only move oxygen, not nutrients or wastes, so a second transport route is needed
   • Diffusion stops completely in animals above a certain body mass, so blood must replace it
   • Diffusion is too slow to supply the cells of a large body over the distances involved

2. What is mass transport?

   • Movement of individual molecules across a membrane from high to low concentration without any input of energy
   • Movement of water across a partially permeable membrane from a dilute solution to a concentrated solution
   • Active uptake of ions against a concentration gradient using ATP released by respiration in the cell
   • Bulk movement of substances over large distances, usually in a moving fluid carried by a transport system

3. Which property of water is the main reason it is an effective solvent for ionic and polar substances?

   • Its molecules are polar, so they surround and separate ions and other polar molecules
   • Its molecules are joined by strong covalent bonds that stop them being pulled apart by dissolved ions
   • Its molecules have no hydrogen bonds, so they move freely past dissolved solutes without attraction
   • Its molecules are non-polar, so they pack closely around large lipid molecules in solution

4. A water molecule is described as a dipole. What does this mean?

   • The molecule has two oxygen atoms bonded to one hydrogen atom, which gives it a net negative charge
   • The molecule carries a full positive charge on its hydrogen atoms and a full negative charge on its oxygen atom
   • One end has a partial positive charge and the other a partial negative charge because shared electrons are pulled towards oxygen
   • The molecule is held together by ionic bonds between its oxygen atom and its two hydrogen atoms

5. Hydrogen bonds form between water molecules. Between which atoms do they form?

   • A hydrogen atom of one molecule and a hydrogen atom of a neighbouring molecule sharing electrons
   • Two hydrogen atoms from neighbouring molecules that both carry a full positive charge
   • The oxygen atoms of two neighbouring molecules that both carry a full negative charge
   • A partially positive hydrogen atom of one molecule and a partially negative oxygen atom of a neighbouring molecule

6. As an organism's size increases, what happens to its surface area to volume ratio?

   • It stays constant because surface area and volume increase by the same proportion
   • It decreases, so the surface may be too small to meet the needs of the whole volume
   • It increases, so exchange surfaces become more efficient at supplying the whole volume
   • It increases only in organisms that have a circulatory system, which keeps exchange efficient

7. Which feature of blood plasma makes it an effective transport medium?

   • It is made of insoluble proteins that carry solutes physically in suspension without dissolving them
   • It is made mainly of red blood cells, which carry dissolved solutes in their cytoplasm only
   • It contains very little water, so it can carry large non-polar lipids without dissolving them
   • It is mostly water, which dissolves many substances such as glucose, ions and urea for transport

8. A spherical organism's radius doubles. Approximately how does its surface area to volume ratio change?

   • It doubles
   • It halves
   • It quadruples
   • It stays the same

9. A cube has sides of 4 cm. What is its surface area to volume ratio?

   • 1.5 per cm
   • 0.67 per cm
   • 3 per cm
   • 6 per cm

10. The diffusion distance across a tissue doubles. Roughly how does the time taken for diffusion change?

    • It decreases by a factor of about two
    • It increases by a factor of about two
    • It increases by a factor of about four
    • It increases by a factor of about eight

11. What is the relative formula mass of water, H2O? (Ar: H = 1, O = 16)

    • 16
    • 20
    • 18
    • 10

12. A cube with sides of 1 cm is compared with a cube with sides of 3 cm. Which statement about the larger cube is correct?

    • Its surface area to volume ratio is three times that of the smaller cube
    • Its surface area to volume ratio is the same as that of the smaller cube
    • Its surface area to volume ratio is one third that of the smaller cube
    • Its surface area to volume ratio is nine times that of the smaller cube

13. Why does the dipole nature of water matter for transport in a mammal?

    • It allows water to move through the body only as a gas, which avoids the need for dissolved transport
    • It lets water dissolve polar and ionic solutes such as glucose and sodium ions so they can be carried in blood
    • It makes water non-polar so it can carry lipids through membranes without any help from carrier proteins
    • It stops the blood from freezing in cold conditions by binding all dissolved ions into hydrogen bonds

14. Why can a single-celled amoeba exchange substances with its environment without a circulatory system, while a blue whale needs one?

    • Amoebae are unicellular, so they need no oxygen, whereas the multicellular whale needs a great deal of oxygen
    • Amoebae store all the nutrients they need in vacuoles, so they never need to transport anything between cells
    • A small size gives a large surface area to volume ratio, so diffusion across the surface meets the cell's needs
    • Whales have a larger surface area to volume ratio, so they need a pump to move blood faster around the body

15. A 1 g shrew and a 70 kg human are compared. Why does the shrew lose heat per gram much faster?

    • Its blood contains more haemoglobin per gram, so it produces more ATP and loses more heat
    • Its cells are larger, so each cell respires more quickly and releases more heat energy
    • It has a larger surface area to volume ratio, so it loses heat quickly relative to its mass
    • It has a lower proportion of water in its tissues, so its tissues conduct heat away more easily

16. A cube-shaped organism has sides of 2 cm and grows to sides of 6 cm. What happens to its surface area to volume ratio?

    • It stays the same because the shape of the organism has not changed
    • It falls to one ninth of its original value
    • It triples because the surface area increases by a factor of nine
    • It falls to one third of its original value

17. Which statement about the transport of oxygen in mammalian blood is most accurate?

    • It is carried entirely dissolved in plasma because oxygen is a non-polar gas that dissolves well in water
    • Most dissolves directly in plasma because plasma is mostly water and oxygen is a polar molecule
    • Only a small fraction dissolves in plasma, and most is carried bound to haemoglobin in red blood cells
    • It is carried only as ions dissolved in plasma, bound to sodium ions that move it through the circulation

18. Why do hydrogen bonds between water molecules raise water's boiling point compared with similar small molecules?

    • Hydrogen bonds between water molecules make water a gas at room temperature, which raises its boiling point
    • More energy is needed to break the many hydrogen bonds between molecules before they can escape as a gas
    • Hydrogen bonds are covalent bonds that hold each water molecule intact, so molecules cannot separate easily
    • Hydrogen bonds form only in ice, so liquid water has no bonding between molecules to overcome

19. Which change would most increase the rate of diffusion across a surface, according to Fick's Law?

    • Reducing the concentration difference across the surface to zero so that no net movement occurs
    • Decreasing the surface area while increasing the thickness of the membrane at the same time
    • Increasing the surface area and steepening the concentration gradient across the surface
    • Doubling the thickness of the surface while keeping the concentration gradient constant

20. Why must an exchange surface such as an alveolus be very thin?

    • A thin surface has a larger surface area to volume ratio, which means it holds more gas at once
    • A thin surface allows the gas to be pumped across the membrane by the heart at higher pressure
    • A short diffusion distance gives a steeper, faster diffusion gradient across the surface
    • A thin surface prevents red blood cells from entering the capillary, which keeps blood flowing smoothly

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