Cell Biology — Chapter 4 notes.pdf

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1. 1

   Which structure controls what enters and leaves the cell?

   • a)Cell wall
   • b)Cell membrane
   • c)Nucleus
   • d)Cytoplasm

   The membrane is selectively permeable — it decides what crosses.

2. 2

   Where in the cell is most ATP produced?

   • a)Ribosome
   • b)Golgi apparatus
   • c)Mitochondrion
   • d)Lysosome

   Aerobic respiration happens in the mitochondria, which release most of the cell’s ATP.

3. 3

   Which organelle is the site of protein synthesis?

   • a)Ribosome
   • b)Vacuole
   • c)Chloroplast
   • d)Nucleolus

   Ribosomes read mRNA and assemble amino acids into polypeptides.

4. 4

   Movement of water across a partially permeable membrane, from high to low water potential, is called:

   • a)Diffusion
   • b)Osmosis
   • c)Active transport
   • d)Phagocytosis

   Osmosis is the specific case for water down a water-potential gradient.

5. 5

   Which process moves substances AGAINST a concentration gradient and therefore requires ATP?

   • a)Osmosis
   • b)Facilitated diffusion
   • c)Active transport
   • d)Simple diffusion

   Only active transport pumps against the gradient, so only it costs energy.

6. 6

   How many daughter cells does one round of mitosis produce?

   • a)One
   • b)Two
   • c)Four
   • d)Eight

   Mitosis produces two genetically identical diploid daughter cells.

7. 7

   Meiosis differs from mitosis chiefly because it:

   • a)Produces identical diploid cells
   • b)Halves the chromosome number and creates genetic variation
   • c)Occurs only in bacteria
   • d)Requires no DNA replication

   Meiosis halves chromosome number and shuffles alleles by crossing over and independent assortment.

8. 8

   Which pigment absorbs the light used in photosynthesis?

   • a)Haemoglobin
   • b)Chlorophyll
   • c)Melanin
   • d)Keratin

   Chlorophyll in the chloroplast absorbs mainly red and blue light.

9. 9

   The balanced equation for photosynthesis is $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$. What is the role of light?

   • a)It is a reactant consumed in the equation
   • b)It supplies the energy that drives the reaction
   • c)It is a product of the reaction
   • d)It acts as a catalyst that is chemically changed

   Light is the energy input, which is why it sits above the arrow rather than in the equation.

10. 10

    Raising temperature well above an enzyme’s optimum reduces the rate of reaction because the enzyme:

    • a)Becomes more concentrated
    • b)Is denatured, changing its active site
    • c)Reacts with the substrate permanently
    • d)Turns into a substrate

    Heat breaks the bonds holding the tertiary structure, so the active site no longer fits the substrate.

11. 11

    An enzyme lowers the activation energy of a reaction. This means it:

    • a)Makes the reaction release more energy overall
    • b)Provides an alternative route with a lower energy barrier
    • c)Changes the equilibrium position in favour of products
    • d)Is consumed in proportion to the substrate

    A catalyst changes the route, not the overall energy change or the equilibrium position.

12. 12

    A section of DNA that codes for one polypeptide is called a:

    • a)Chromosome
    • b)Gene
    • c)Nucleotide
    • d)Ribosome

    A gene is the coding unit; a chromosome carries many genes.

13. 13

    Two heterozygous parents (Bb × Bb) are crossed. What fraction of offspring is expected to show the recessive phenotype?

    • a)$\frac{1}{2}$
    • b)$\frac{1}{4}$
    • c)$\frac{3}{4}$
    • d)None

    The Punnett square gives BB : Bb : bb as 1 : 2 : 1, so bb is one in four.

14. 14

    Why do root hair cells have a large surface area?

    • a)To increase the rate of water and mineral uptake
    • b)To store more starch
    • c)To photosynthesise faster
    • d)To reduce respiration

    A larger surface area increases the rate of absorption across the membrane.

15. 15

    During vigorous exercise, muscle cells respire anaerobically. The product that causes fatigue is:

    • a)Ethanol
    • b)Lactic acid
    • c)Carbon dioxide only
    • d)Glucose

    In animals, anaerobic respiration converts glucose to lactic acid, which accumulates and causes an oxygen debt.

16. 16

    Which of these is found in a plant cell but NOT in an animal cell?

    • a)Mitochondrion
    • b)Cell wall
    • c)Nucleus
    • d)Cell membrane

    A cellulose cell wall is a plant feature; the other three are in both.