Key ideas flashcards

Topic 8: Key ideas

Photosynthesis vs respiration: endothermic or exothermic?

Photosynthesis is endothermic: it takes in energy from light. Respiration is exothermic: it transfers energy to the environment.

Surface area to volume ratio of a 2 cm cube

SA = 6 × 2 × 2 = 24 cm²; V = 8 cm³; ratio = 3 : 1. A bigger organism has more surface area in total but a smaller ratio.

Why is starch a good storage molecule, and what is a lipid made of?

Starch is insoluble. A lipid is made of one glycerol and three fatty acids.

How many bases code for a protein of 120 amino acids?

120 × 3 = 360 bases.

Grass holds 4000 g of biomass; the sheep eating it hold 360 g. Efficiency?

360 ÷ 4000 × 100 = 9%.

What does a plant need, besides glucose, to make amino acids?

Nitrate ions absorbed from the soil.

Three uses of energy transferred by respiration

Building larger molecules, movement, and keeping warm.

Why does high biodiversity make an ecosystem more stable?

Many species share the work of providing food, shelter and pollination, so losing one species has a smaller effect on the community.

Genetically identical plants grow differently in different soils. What does this show?

Characteristics depend on the genome and the environment; here the variation is environmental only.

Why say an enzyme is "denatured", not "killed", at high temperature?

Enzymes are not alive. The active site changes shape, so the substrate no longer fits.

How can a mutation change how a protein works?Higher

A change in the DNA can change the protein's shape, so an enzyme's active site may no longer fit its substrate, or a structural protein may lose its strength. Variants in non-coding DNA can alter gene expression.