Biology A 3, Biology A 2.

Biology A 3, Biology A 2
Give two examples of biological molecules containing nitrogen that would be removed when
a crop is harvested. [2 marks]
1. Amino acid;
2. Nucleic acid;
3. DNA;
4. RNA;
5. ATP;
6. NAD/NADP;
7. Cyclic AMP/cAMP;
8. Chlorophyll;


Outline a method the ecologists could have used to determine the plant species richness at
one site. [3 marks]
1. A method of selecting sampling sites at random;
2. Use of quadrat;
3. Identify plant species in each quadrat;

Name two enzymes involved in the semi-conservative replication of DNA. [2 marks]
1. DNA helicase;
2. DNA polymerase;


Sometimes, damage occurs during DNA replication. One enzyme involved in repairing
damage to DNA is called ATR. ATR works as follows:
• ATR phosphorylates other enzymes involved in repairing DNA.
• ATR also phosphorylates substrates required to repair DNA.
When ATR phosphorylates other enzymes, these enzymes become able to bind to their
substrates. Use your knowledge of enzyme structure to suggest why. [2 marks]
1. Changes tertiary structure of the enzyme;
2. Active site becomes complementary;


The enzyme-catalysed reactions activated by ATR only occur if the substrates have been
phosphorylated. Use your knowledge of energy changes in enzyme-catalysed reactions to
suggest why. [1 mark]
Phosphorylation lowers activation energy for the reaction


The rate of water movement through a shoot in a potometer may not be the same as the rate
of water movement through the shoot of a whole plant. Suggest one reason why. [1 mark]
Plant has roots

,The importance of nitrogen-containing substance in biological systems:

Nitrogen cycle:

- Nitrogen fixation, ammonification, nitrification, denitrification

- Importance: organisms cannot obtain nitrogen from the nitrogen cycle, nitrogen is needed
for nucleic acids

Photosynthesis:

- NADP and ATP, enzymes used in respiration (rubisco)

- Importance: produce organic sugars which can be passed on by biomass

Respiration:

- NAD and ATP, coenzyme A and citrate synthase

- Importance: provide ATP for energy requiring processes

Proteins and enzymes:

- Nitrogen in proteins so enzymes

- Importance: catalases enzyme controlled reactions




The importance of diffusion in organisms:

Gas exchange:

- Oxygen diffuses down and pressure and concentration gradient; countercurrent
mechanism

- Importance: obtain oxygen needed for oxidative phosphorylation

Photosynthesis:

- H+ ions diffuse down a concentration gradient through ATP synthase to produce ATP in the
electron transport chain

- Importance: produced the ATP needed for LIR

Respiration:

- H+ ions diffuse through ATP synthase to produce ATP in oxidative phosphorylation

, - Importance: to produce large amounts of ATP for metabolic processes

Digestion and absorption:

- Cotransport of Na+ out of the epithelial cells to create a concentration gradient, Na+ move
in by facilitated diffusion bringing glucose or amino acids with them

- Importance: respiration or protein synthesis




If most of the mitochondria in a cell are faulty, this prevents many important
enzyme-catalysed reactions taking place or slows them down. Suggest and explain one
reason why. [2 marks]
1. Not enough ATP produced;
2. ATP provides energy for enzyme reactions;


Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen
molecule to bind. Explain why. [2 marks]
1. Binding of first oxygen changes tertiary structure of haemoglobin;
2. Creates another binding site;


When counting, cells that touch top or left lines are counted but cells that touch right or
bottom lines are not counted. Suggest two reasons for this rule. [2 marks]
1. To avoid dealing with parts of cells;
2. To avoid counting same cells twice;
3. To get comparable results;


The scientists began by lysing (breaking open) cells and organelles using a detergent that
dissolves lipids in water. Suggest how the detergent releases CENP-W from cells. [2 marks]
1. Cell membranes made from phospholipid;
2. Detergent dissolves phospholipid bilayer;


Explain how ultracentrifugation separates CENP-W from other molecules.
[2 marks]
1. Spin supernatant at very high speed;
2. Molecules separates depending on molecular mass;


The scientists used units of μg g−1 for the concentration of ammonia in soil.
Suggest why, in this investigation, the scientists used these units. [2 marks]
1. (µg because) very little ammonia in soil;
3. (g -1 ) to allow comparisons between samples;