Cellular respiration

Question 1

Photosynthesis

Answer 1

Photosynthesis is the biological process by which green plants, algae, and some bacteria convert light energy, usually from the sun, into chemical energy stored in glucose molecules. This process involves the absorption of light by chlorophyll in chloroplasts, which triggers a series of chemical reactions that produce glucose and release oxygen as a biproduct.

Question 2

Autotrophs

Answer 2

An autotroph is an organism that can produce its own food using inorganic substances, such as carbon dioxide and water, and an external energy source, typically sunlight or chemical energy.

Question 3

Heterotrophs

Answer 3

Heterotrophs are organisms that are unable to produce their own food and thus rely on consuming organic matter produced by other organisms to obtain energy and nutrients for growth and survival.

Question 4

Chemical cycling between photosynthesis and cellular respiration

Answer 4

Photosynthesis converts carbon dioxide and water into glucose and oxygen using light energy. Cellular respiration breaks down glucose to produce ATP, releasing carbon dioxide and water. Oxygen from photosynthesis is used in cellular respiration, while carbon dioxide from respiration can be used in photosynthesis, creating a continuous cycle of key chemicals.

Question 5

Aerobic respiration

Answer 5

Aerobic respiration is the process by which cells use oxygen to break down glucose into ATP, releasing carbon dioxide and water as byproducts. It occurs in the mitochondria and is the main energy-producing pathway in most organisms.

Question 6

Anaerobic respiration

Answer 6

Anaerobic respiration is the process by which cells break down glucose to produce energy without using oxygen. It is less efficient than aerobic respiration and can produce lactic acid or ethanol as byproducts.

Question 7

Cellular respiration

Answer 7

Metabolic process by which cells break down organic molecules, typically glucose, to produce energy in the form of ATP (adenosine triphosphate). This process occurs in all living cells and involves several stages, including glycolysis, the citric acid cycle (Krebs cycle), and the electron transport chain.

Question 8

Glycolysis

Answer 8

Glycolysis is the initial metabolic pathway in cellular respiration, occurring in the cytoplasm of cells, where glucose is converted into pyruvate molecules. This process generates a small amount of ATP and NADH, which serve as energy carriers for subsequent stages of cellular respiration.

Step-by-Step Process:

Glucose Priming: Glucose, a six-carbon sugar molecule, is phosphorylated and primed for breakdown into smaller molecules.
Splitting: Glucose is split into two three-carbon molecules called glyceraldehyde-3-phosphate (G3P).

Energy Extraction: Each G3P molecule undergoes oxidation, producing two molecules of NADH and ATP through substrate-level phosphorylation.

Pyruvate Formation: G3P is converted into pyruvate, a three-carbon molecule, resulting in the net production of two molecules of pyruvate, two molecules of ATP, and two molecules of NADH.

Net Outcome: The net yield of glycolysis per glucose molecule is two molecules of pyruvate, two molecules of ATP (generated through substrate-level phosphorylation), and two molecules of NADH, along with the release of hydrogen ions (H+) and water molecules.

Question 9

Citric acid cycle

Answer 9

The citric acid cycle, occurring in the mitochondria, is a series of biochemical reactions that convert acetyl-CoA into ATP, NADH, and FADH₂, essential for cellular respiration.

Step-by-Step Process:

1. Acetyl-CoA combines with oxaloacetate to form citrate.
2. Citrate is converted to isocitrate.
3. Isocitrate is oxidized to α-ketoglutarate, producing NADH and CO₂.
4. α-ketoglutarate is oxidized to succinyl-CoA, yielding NADH and CO₂.
5. Succinyl-CoA generates GTP (convertible to ATP) and CoA.
6. Succinate is oxidized to fumarate, producing FADH₂.
7. Fumarate is hydrated to malate.
8. Malate is oxidized to regenerate oxaloacetate, yielding NADH.
9. Overall, the cycle produces ATP (or GTP), NADH, FADH₂, and CO₂, which participate in further energy production.

Question 10

Electron transport chain

Answer 10

The electron transport chain (ETC) is a series of protein complexes in the inner mitochondrial membrane that use electrons from molecules like NADH and FADH₂ to make ATP, the cell’s energy currency.

Step-by-Step Process:

Electron Donation: NADH and FADH₂ donate electrons.

Complexes I and II: Electrons move through protein complexes I and II, pumping protons.

Coenzyme Q: Electrons move to coenzyme Q.

Complex III: Electrons pass through complex III to cytochrome c, pumping more protons.

Cytochrome c: Electrons move to cytochrome c.

Complex IV: Electrons go through complex IV to oxygen, creating water and pumping more protons.

Proton Gradient: Protons build up in the intermembrane space.
ATP Synthase: Protons flow back through ATP synthase, making ATP.

ATP Production: ATP is made using the energy from proton flow.

Overall Outcome: The ETC creates a proton gradient, driving ATP production, which is crucial for cell energy.

Question 11

Fermentation

Answer 11

Fermentation is an anaerobic metabolic process related to cellular respiration, where microorganisms break down sugars into simpler substances, such as ethanol or lactic acid, to generate energy in the absence of oxygen. While cellular respiration produces more ATP per molecule of glucose in aerobic conditions, fermentation is utilized when oxygen is scarce, allowing cells to continue producing energy.