20 Identify the following blood components, 21 Which is the order of events during aerobic cellular respiration? 22 Which of the following is correct about DNA and RNA? 23 A black bull was crossed to a white cow. The progeny had a black and white coat. Identify

here are the answers to the questions:

20. Identify the following blood components.

• (i) is a biconcave disc, characteristic of a red blood cell (erythrocyte).
• (ii) is an irregular, spiky cell, which could represent a phagocyte (like a neutrophil or macrophage) or an activated lymphocyte.
• (iii) is a small, irregular cell fragment, characteristic of a platelet (thrombocyte).
• (iv) is a cell with a large, relatively round nucleus and less cytoplasm, characteristic of a lymphocyte.

Given the options, there appears to be some ambiguity or potential error in the question's mapping of images to the table columns. However, we must choose the best fit.
Let's assume the most distinct identifications: (i) is a red blood cell, and (iii) is a platelet.
Looking at the options, only option A starts with (I) red blood cells. Let's evaluate option A:

• (I) red blood cells - Matches image (i).
• (II) lymphocytes - Image (ii) is spiky, often associated with phagocytes, but some lymphocytes can be irregular.
• (III) phagocytes - Image (iii) is clearly a platelet, not a phagocyte. This is a mismatch.
• (IV) platelets - Image (iv) is clearly a lymphocyte, not a platelet. This is a mismatch.

Due to the clear mismatches for (III) and (IV) in option A, and the fact that no other option correctly identifies (I) as red blood cells, this question is problematic. However, if forced to choose the best option, and assuming (i) is correctly identified, then there might be an intended mapping that deviates from standard representations for (ii), (iii), and (iv).
Given the common representations, the most accurate identification for (i) is red blood cell, (iii) is platelet, and (iv) is lymphocyte. Image (ii) is most likely a phagocyte. None of the options perfectly align with these standard identifications.
If we consider the possibility that (ii) is a lymphocyte and (iii) is a phagocyte, and (iv) is a platelet, then option A would be the intended answer, despite the visual discrepancies for (iii) and (iv).

The correct option is A. (Acknowledging the visual ambiguity in the question's images and options).

21. Which is the order of events during aerobic cellular respiration?
Aerobic cellular respiration starts with glucose.

1. Glycolysis: Glucose (6-carbon) is broken down into two molecules of pyruvate (3-carbon). This process involves intermediate steps like triose phosphate.
2. Pyruvate oxidation: Pyruvate is converted to acetyl-CoA.
3. Krebs cycle (Citric Acid Cycle): Acetyl-CoA enters the Krebs cycle.
4. Oxidative phosphorylation (Electron Transport Chain): This is where most ATP is produced, consuming oxygen and producing water.

Let's evaluate the options:

• A: glucose $\to$ triose phosphate $\to$ pyruvate $\to$ Krebs cycle $\to$ $\text{CO}_2 + \text{H}_2\text{O} + \text{ATP}$. This correctly outlines the main stages and products.
• B: glucose $\to$ triose phosphate $\to$ pyruvate $\to$ Krebs cycle $\to$ $\text{CO}_2 + \text{H}_2\text{O} + \text{ADP} + \text{Pi}$. This is also correct, as ATP is formed from ADP + Pi.
• C: glucose $\to$ hexose phosphate $\to$ pyruvate $\to$ Krebs cycle $\to$ $\text{CO}_2 + \text{H}_2\text{O} + \text{ADP} + \text{Pi}$. Hexose phosphate is an intermediate in glycolysis before triose phosphate. This is also a plausible pathway.
• D: glucose $\to$ hexose phosphate $\to$ pyruvate $\to$ Krebs cycle $\to$ $\text{CO}_2 + \text{ethanol} + \text{ATP}$. Ethanol is a product of anaerobic respiration (fermentation), not aerobic respiration.

Options A, B, and C describe correct pathways. However, option A and B are more general and represent the overall process. Option A states ATP as a product, which is the final energy currency. Option B states ADP + Pi, which are the precursors. Both are technically correct. Option C includes hexose phosphate, which is an earlier intermediate. Usually, the overall summary focuses on glucose to pyruvate.
Between A and B, A is a more direct statement of the final energy product.

The correct option is A.

22. Which of the following is correct about DNA and RNA?
Let's analyze the components of DNA and RNA:

• Bases: DNA has Adenine (A), Guanine (G), Cytosine (C), and Thymine (T). RNA has Adenine (A), Guanine (G), Cytosine (C), and Uracil (U). So, DNA has Thymine, RNA has Uracil.
• Sugar: DNA has Deoxyribose sugar. RNA has Ribose sugar.

Let's check the options:

• A: RNA Base: Thymine (Incorrect, RNA has Uracil). DNA Base: Uracil (Incorrect, DNA has Thymine). RNA Sugar: Ribose (Correct). DNA Sugar: Deoxyribose (Correct).
• B: RNA Base: Uracil (Correct). DNA Base: Thymine (Correct). RNA Sugar: Ribose (Correct). DNA Sugar: Deoxyribose (Correct).
• C: RNA Base: Uracil (Correct). DNA Base: Thymine (Correct). RNA Sugar: Deoxyribose (Incorrect, RNA has Ribose). DNA Sugar: Ribose (Incorrect, DNA has Deoxyribose).
• D: RNA Base: Thymine (Incorrect, RNA has Uracil). DNA Base: Uracil (Incorrect, DNA has Thymine). RNA Sugar: Deoxyribose (Incorrect, RNA has Ribose). DNA Sugar: Ribose (Incorrect, DNA has Deoxyribose).

The only option where all four components (RNA base, DNA base, RNA sugar, DNA sugar) are correctly identified is B.

23. A black bull was crossed to a white cow. The progeny had a black and white coat. Identify
This question is incomplete. It asks to "Identify" something but the sentence cuts off. Based on the description "black and white coat", it likely refers to a pattern like roan or spotted, which indicates codominance or incomplete dominance. The question would typically ask to identify the type of inheritance or the genotypes involved. Without the full question, a complete answer cannot be provided.