name and describe five ways substances can move across the cell surface membrane into a cell (5 marks)
1. (Simple) diffusion of small/non-polar molecules down a
concentration gradient;
2. Facilitated diffusion down a concentration gradient via
protein carrier/channel;
3. Osmosis of water down a water potential gradient;
4. Active transport against a concentration gradient via
protein carrier using ATP;
5. Co-transport of 2 different substances using a carrier
protein;
describe the structure of DNA (5 marks)
1. Polymer of nucleotides;
2. Each nucleotide formed from deoxyribose, a
phosphate (group) and an organic/nitrogenous base;
3. Phosphodiester bonds (between nucleotides);
4. Double helix/2 strands held by hydrogen bonds;
5. (Hydrogen bonds/pairing) between adenine, thymine
and cytosine, guanine;
describe how a triglyceride molecule if formed (3 marks)
1. One glycerol and three fatty acids;
2. Condensation (reactions) and removal of
three molecules of water;
3. Ester bond(s) (formed);
Describe and explain two features you would expect to find in a cell specialised for absorption
1. Folded membrane/microvilli so large surface
area (for absorption);
2. Large number of
co-transport/carrier/channel proteins so fast
rate (of absorption)
OR
Large number of co-transport/carrier proteins
for active transport
OR
Large number of
co-transport/carrier/channel proteins for
facilitated diffusion;
3. Large number of mitochondria so make
(more) ATP (by respiration)
OR
Large number of mitochondria for aerobic
respiration
OR
Large number of mitochondria to release
energy for active transport;
4. Membrane-bound (digestive) enzymes so
maintains concentration gradient (for fast
absorption);
Describe the role of micelles in the absorption of fats into the cells lining the ileum.
1. Micelles include bile salts and fatty acids;
2. Make the fatty acids (more) soluble in water;
3. Bring/release/carry fatty acids to cell/lining (of the
ileum);
4. Maintain high(er) concentration of fatty acids to
cell/lining (of the ileum);
5. Fatty acids (absorbed) by diffusion;