Question
The electron micrograph shows part of a cell including a mitochondrion.
a. Outline how the structures labelled X and Y are adapted to carry out the function of the mitochondrion.
X:
Y: [2]
b. Explain how ATP is generated in mitochondria by chemiosmosis. [4]
▶️Answer/Explanation
Ans:
a. Outline how the structures labelled X and Y are adapted to carry out the function of the mitochondrion. [2]
X: Inner membrane is folded into cristae, increasing surface area for electron transport and ATP synthesis.
Y: Matrix contains enzymes for the Krebs cycle and link reaction.
b. Explain how ATP is generated in mitochondria by chemiosmosis. [4]
- Electrons pass through the electron transport chain in the inner membrane.
- This energy pumps protons into the intermembrane space, creating a proton gradient.
- Protons diffuse back into the matrix through ATP synthase.
- This drives ATP production from ADP and Pi.
Question
a. Outline the functions of rough endoplasmic reticulum and Golgi apparatus. [3]
b. Outline the control of metabolism by end-product inhibition. [5]
c. Explain how hydrophobic and hydrophilic properties contribute to the arrangement of molecules in a membrane. [7]
▶️Answer/Explanation
a. Outline the functions of rough endoplasmic reticulum and Golgi apparatus. [3 marks]
- Rough endoplasmic reticulum (RER) synthesizes proteins using ribosomes on its surface.
- RER packages proteins into vesicles for transport.
- Golgi apparatus modifies, sorts, and packages proteins for secretion or delivery within the cell.
b. Outline the control of metabolism by end-product inhibition. [5 marks]
- End-product inhibition is a type of negative feedback in metabolic pathways.
- The final product of a pathway binds to the first enzyme (usually allosterically).
- This binding changes the enzyme’s shape, reducing its activity.
- This slows or stops the pathway when the product is abundant.
- When product levels drop, inhibition is removed, and the pathway resumes.
c. Explain how hydrophobic and hydrophilic properties contribute to the arrangement of molecules in a membrane. [7 marks]
- Phospholipids form the main structure of membranes.
- Each phospholipid has a hydrophilic (water-attracting) head and hydrophobic (water-repelling) tails.
- In water, phospholipids arrange into a bilayer.
- Hydrophilic heads face the outside (toward water), and hydrophobic tails face inward (away from water).
- This arrangement creates a semi-permeable membrane.
- It allows nonpolar molecules to pass while restricting polar or charged ones.
- This structure supports membrane fluidity and selective transport.