Plant vs animal cell structure
Both plant and animal cells share a nucleus (controls the cell and holds genetic material), cytoplasm (where many reactions happen), cell membrane (controls what enters/leaves), and mitochondria (release energy via respiration). Plant cells additionally have a rigid cell wall (support), chloroplasts (photosynthesis), and a large permanent vacuole (storage and support) -- structures animal cells lack.
Movement across membranes
Diffusion moves particles from high to low concentration and needs no energy -- like a gas spreading through a room. Osmosis is the same idea applied specifically to water crossing a selectively permeable membrane. Active transport moves particles the "wrong way," from low to high concentration, which is why it needs energy (usually from respiration).
Example 1: Root hair cells absorb mineral ions from soil even when the ions are more concentrated inside the cell than in the soil. Which transport process is this, and why?
This is active transport -- moving ions against their concentration gradient (low outside, high inside) requires the cell to spend energy, unlike diffusion or osmosis which happen passively down a gradient.
Enzymes
Enzymes are biological catalysts that speed up specific reactions by lowering the energy needed to start them, without being used up themselves. Each enzyme has a specific shape that fits its substrate (the "lock and key" model). Enzymes work best within a narrow temperature and pH range; too much heat permanently changes (denatures) their shape, destroying their activity.
Example 2: An enzyme's activity drops sharply above 45°C and does not recover even after cooling back down. Explain why.
High temperature disrupts the enzyme's precise 3D shape (denaturation), including its active site. Since the enzyme's action depends entirely on that shape fitting its substrate, once the shape is permanently destroyed the enzyme can no longer function, even after cooling.
Biomolecules
Carbohydrates are the body's main energy source. Proteins are needed for growth, repair, and making enzymes/hormones. Lipids (fats and oils) store energy long-term and provide insulation. A balanced diet needs all three in the right proportions, alongside vitamins, minerals, fibre, and water.