Sure! Below is a test format based on the specified topics related to photoperiodism, control of flowering, and the switching mechanism of phytochrome. Each section includes questions along with their corresponding marks and answers.
Test Format: Biology - Photoperiodism and Related Topics
Total Marks: 100
Section 1: Photosynthesis (25 marks)
Question 1 (10 marks)
Explain the process of photosynthesis, including the light-dependent and light-independent reactions.
Answer:
Photosynthesis occurs in two main stages:
-
Light-dependent reactions (occurring in thylakoid membranes): These reactions capture sunlight, using chlorophyll to absorb light energy, leading to the splitting of water (photolysis) and the release of oxygen. Energy from sunlight is converted into ATP and NADPH.
-
Light-independent reactions (Calvin Cycle) (occurring in the stroma): ATP and NADPH produced in the light-dependent reactions are used to convert carbon dioxide (CO2) into glucose (C6H12O6) through a series of enzymatic reactions. This process does not require light directly.
Section 2: Cellular Respiration (19 marks)
Question 2 (9 marks)
Describe the main stages of cellular respiration.
Answer:
Cellular respiration consists of four main stages:
- Glycolysis: Occurs in the cytoplasm, where glucose is broken down into pyruvate, producing ATP and NADH.
- Pyruvate Oxidation: Pyruvate is transported into the mitochondria and converted into Acetyl CoA, releasing CO2.
- Krebs Cycle: Acetyl CoA enters the cycle, producing ATP, NADH, and FADH2, while releasing CO2.
- Electron Transport Chain: NADH and FADH2 donate electrons, which are transported through protein complexes in the inner mitochondrial membrane, generating a proton gradient and ultimately producing ATP through oxidative phosphorylation.
Section 3: Plant Responses to Internal and External Stimuli (43 marks)
Question 3 (15 marks)
What is photoperiodism, and how does it influence the flowering of plants?
Answer:
Photoperiodism is the physiological reaction of organisms to the length of day or night. In plants, it primarily refers to how variations in day length trigger flowering.
- Short-day plants require longer nights to flower, while long-day plants need shorter nights.
- Plants perceive light through a pigment called phytochrome, which exists in two forms: Pr (inactive) and Pfr (active). The level of Pfr, which accumulates in light and converts back to Pr in darkness, informs the plant of day length, thus initiating the flowering hormone (florigen) production when the required photoperiod is met.
Question 4 (14 marks)
Explain the function of phytochrome in plants and its role in regulating flowering and other responses.
Answer:
Phytochrome is a photoreceptive protein that regulates plant responses to light. It exists in two interconvertible forms:
- Pr (red light-absorbing form): Absorbs red light, converting to Pfr.
- Pfr (far-red light-absorbing form): Absorbs far-red light. It influences various growth processes, including seed germination, stem elongation, and flowering.
Phytocromes regulate flowering by sensing the duration of light and darkness:
- In long-day plants, an increase in Pfr promotes flowering by triggering the expression of flowering genes, while in short-day plants, a higher ratio of Pr during longer nights prevents flowering.
Section 4: Secondary Metabolites (13 marks)
Question 5 (6 marks)
What are secondary metabolites, and why are they important for plants?
Answer:
Secondary metabolites are organic compounds that are not directly involved in the normal growth, development, or reproduction of plants. They play crucial roles in plant defense against herbivores, pathogens, and UV radiation. Examples include alkaloids (e.g., caffeine), terpenoids (e.g., menthol), and phenolics (e.g., flavonoids). They also attract pollinators and seed dispersers, contributing to ecological interactions and relationships.
Question 6 (7 marks)
List and briefly describe three types of secondary metabolites.
Answer:
- Alkaloids: Nitrogen-containing compounds that often have physiological effects on animals and humans. Examples include caffeine and morphine.
- Terpenoids: A large class of organic chemicals derived from isoprene units; they serve various functions, including plant defense and attraction of pollinators. Examples include menthol and rubber.
- Phenolics: Compounds characterized by the presence of a phenolic ring; they often have antioxidant properties and can deter feeding by herbivores. Examples include flavonoids and tannins.
End of Test
Make sure to review your answers for clarity and comprehensiveness to maximize your marks! Good luck!