Problem 10 - Biology: Science for Life with Physiology

Question

Select the true statement regarding metabolism in plant and animal cells. A. Plant and animal cells both perform photosynthesis and aerobic respiration; B. Animal cells perform aerobic respiration only, and plant cells perform photosynthesis only; C. Plant cells perform aerobic respiration only, and animal cells perform photosynthesis only; D. Plant cells perform cellular respiration and photosynthesis, and animal cells perform aerobic respiration only.

Step-by-Step Solution

Answer

The true statement is D.

Step 1: Understanding the Concepts

First, we need to understand what processes are unique or shared between plant and animal cells. Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy stored as glucose using carbon dioxide and water. This process occurs in plant cells but not in animal cells. Aerobic respiration is the process of breaking down glucose in the presence of oxygen to produce ATP, which is the energy currency of the cell. This process is performed by both plant and animal cells.

Step 2: Evaluating Statement A

Statement A posits that both plant and animal cells perform photosynthesis and aerobic respiration. Since only plant cells can perform photosynthesis, this statement cannot be true for animal cells.

Step 3: Evaluating Statement B

Statement B suggests that animal cells perform only aerobic respiration, while plant cells perform only photosynthesis. This is incorrect because plant cells do both: they perform photosynthesis to make glucose and aerobic respiration to convert glucose into ATP.

Step 4: Evaluating Statement C

Statement C claims that plant cells perform aerobic respiration only, and animal cells perform photosynthesis only. This is incorrect because plant cells perform both photosynthesis and aerobic respiration, whereas animal cells do not perform photosynthesis.

Step 5: Evaluating Statement D

Statement D states that plant cells perform both cellular respiration and photosynthesis, while animal cells perform aerobic respiration only. This accurately describes the metabolic processes occurring in plant and animal cells. Plant cells perform photosynthesis to create glucose and then use aerobic respiration to produce ATP. Animal cells perform only aerobic respiration.

Key Concepts

Photosynthesis

Photosynthesis is a fundamental process carried out by plant cells, algae, and certain bacteria. The whole idea behind photosynthesis is to convert light energy, typically from the sun, into chemical energy stored in glucose molecules. This fascinating transformation happens in the chloroplasts of plant cells.
The main chemical equation for photosynthesis is:

• 6 CO₂ + 6 H₂O + light energy → C₆H₁₂O₆ + 6 O₂

Here’s how it works:

• Light Reaction: This part of photosynthesis captures light energy and uses it to split water molecules, releasing oxygen as a byproduct. It occurs in the thylakoids of the chloroplasts.
• Calvin Cycle: Also known as the dark reaction, it uses carbon dioxide and the ATP and NADPH from the light reaction to produce glucose.

Through photosynthesis, plants not only provide themselves with glucose but also release oxygen into the atmosphere, which is vital for life on Earth.

Aerobic Respiration

Aerobic respiration is a process by which cells convert glucose and oxygen into ATP, the energy currency of the cell, along with carbon dioxide and water. Both animal and plant cells require this pathway to obtain usable energy. The entire process occurs primarily in the mitochondria within cells.
The simplified equation for aerobic respiration is:

• C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + energy (ATP)

Let’s break it down into stages:

• Glycolysis: This occurs in the cytoplasm, where glucose is broken down into pyruvate, producing a small amount of ATP and NADH.
• Krebs Cycle: Also known as the citric acid cycle, this takes place in the mitochondria and produces sugnificant amounts of electron carriers.
• Electron Transport Chain: Electron carriers from glycolysis and the Krebs cycle donate electrons to the chain, leading to the production of water and a larger yield of ATP.

Aerobic respiration is crucial for cellular functions, fueling countless processes by providing the necessary energy.

Plant Cell Metabolism

Plants are unique because they can make their own food and get energy from it, a process known as autotrophy. Plant cell metabolism includes both photosynthesis and respiration. During the day, plants primarily use photosynthesis to make glucose.
Key aspects of plant cell metabolism include:

• Photosynthesis: As mentioned, it occurs in the chloroplasts and converts light energy into glucose.
• Aerobic Respiration: Plant cells perform respiration even during the day to meet energy demands. Respiration occurs in the mitochondria, using the glucose produced.
• Storage and Utilization: Some glucose is stored as starch, while others are used instantly for energy or building other structures like cellulose in the cell wall.

Plant cell metabolism allows plants to grow, repair, and reproduce, all while providing glucose and oxygen for other organisms.

Animal Cell Metabolism

Animal cells depend entirely on external sources for glucose, as they cannot photosynthesize. They rely on consuming organic material to obtain energy through a process primarily driven by aerobic respiration.
Here are key features of animal cell metabolism:

• Aerobic Respiration: Occurs continually in the mitochondria, converting consumed glucose into ATP for energy.
• Energy Usage: Animals use ATP to power everything from movement and growth to reproduction and cell repair.
• Storage: Excess glucose is stored as glycogen in liver and muscle cells, which can be utilized later when needed.

Animal cell metabolism is integral for survival, making energy available for life-sustaining processes at all times.