when plants do not receive enough water their photosynthetic rate drops this is because

HESI A2

HESI A2 Biology Practice Test

1. When plants do not receive enough water, their photosynthetic rate drops. This is because:

A. water is a raw material for the light reactions in photosynthesis
B. carbon dioxide is not available
C. water provides the carbon atoms used to make sugar
D. not enough oxygen is produced to keep fermentation running

Correct answer: A

Rationale: When plants do not receive enough water, their photosynthetic rate drops because water is a raw material required for the light reactions in photosynthesis. In the light reactions, water is split to provide electrons, which are then utilized to produce energy carriers used in converting carbon dioxide into glucose during the Calvin cycle. Therefore, without sufficient water, the light reactions cannot proceed effectively, ultimately leading to a decrease in photosynthetic rate. Choice B is incorrect because carbon dioxide is a separate raw material needed for the Calvin cycle, not the light reactions. Choice C is incorrect as water provides electrons, not carbon atoms, for photosynthesis. Choice D is incorrect because fermentation is not directly related to photosynthesis; oxygen is produced during photosynthesis, not fermentation.

2. Why is DNA important for the metabolic activities of the cell?

A. It initiates cellular mitosis.
B. It provides cell wall stability.
C. It increases glucose absorption.
D. It controls the synthesis of enzymes.

Correct answer: D

Rationale: DNA is important for the metabolic activities of the cell because it controls the synthesis of enzymes. Enzymes are essential for catalyzing metabolic reactions in the cell. Choices A, B, and C are incorrect because DNA is not directly involved in cellular mitosis, cell wall stability, or glucose absorption.

3. The fur color in a population of dogs is controlled by two alleles: black (B) and tan (b). The black allele exhibits complete dominance. If the phenotype of the dog is tan fur, what is its genotype?

A. BB
B. Bb
C. bb
D. Not enough information

Correct answer: C

Rationale: The correct answer is C: "bb." Since tan fur is the recessive trait controlled by the allele 'b,' the only possible genotype for a dog with tan fur is 'bb.' If a dog had the genotype 'BB' or 'Bb,' the dominant trait (black fur) would be expressed, not tan fur. Choice D, 'Not enough information,' is incorrect because based on the information provided, we can deduce the genotype of a dog with tan fur.

4. Which is not a step in the water cycle?

A. Condensation
B. Transpiration
C. Nitrification
D. Absorption

Correct answer: C

Rationale: Nitrification is a biological process in the nitrogen cycle where ammonia is converted into nitrites and then nitrates by bacteria. It is not a step in the water cycle. The water cycle involves processes like evaporation, condensation, precipitation, and transpiration that are related to the movement and transformation of water in the environment. Choices A, B, and D are all part of the water cycle: condensation is the process where water vapor turns into liquid water, transpiration is the release of water vapor by plants, and absorption refers to the process of water being taken in by soil or other materials.

5. What is the composition of the plasma membrane?

A. Proteins
B. Lipids
C. Carbohydrates
D. Nucleotides

Correct answer: B

Rationale: The plasma membrane is composed of lipids, proteins, and carbohydrates. While proteins are an essential component of the plasma membrane, it is not the only constituent. Carbohydrates and lipids also play crucial roles in the structure and function of the plasma membrane. Nucleotides are not part of the primary structural components of the plasma membrane, making this choice incorrect.