4 Marker Questions

Algal Bloom

1. Nitrates/fertilisers leach into fresh water, causing an increase in algal populations.

2. The Algal bloom reduces light levels, which stops plants at the bottom of the lake from photosynthesising.

3. The plants at the bottom die and are broken down by bacteria.

4. These bacteria multiply and respire, using up large quantities of oxygen in the water, causing other organisms (like fish) to die.

Genetic Engineering

1. Identify the required gene from the source chromosome.

2. Remove the required gene from the source chromosome.

3. Identify the required plasmid from a bacterial cell.

4. Remove the required plasmid from the bacterial cell.

5. Cut open plasmid and insert the required gene.

6. Insert plasmid into new host bacterial cell.

Aerobic respiration in cytoplasm

Glucose is broken down into 2 moles of pyruvate and 2 moles of ATP are produced.

Aerobic respiration in mitochondria

1. Glucose is broken down into 2 moles of pyruvate and 2 moles of ATP are produced.

2. A large number of ATP molecules are produced and carbon dioxide and water are produced.

Active Transport

The movement of molecules of a substance from a region of low concentration to a region of high concentration, against a concentration gradient. This requires energy.

What happens when blood glucose concentration increases?

A change is detected by receptor cells in the pancreas, the pancreas releases more insulin and less glucagon into the blood, then liver cells store more glucose from the blood as glycogen.

What happens when the blood glucose concentration decreases?

A change is detected by the receptor cells in the pancreas, the pancreas releases less insulin and more glucagon into the blood, liver cells breakdown glycogen to release glucose into the blood.

Reflex arc

1. A stimulus is detected by a receptor, sending an electrical impulse.

2. The sensory neuron transmits the impulse towards the central nervous system.

3. A relay (inter) neuron passes the message from the sensory neuron to the motor neuron.

4. The motor neuron carries the impulse to an effector, resulting in a quick response.

Transpiration

1. Transpiration is the loss of water vapor from the leaves of a plant through the stomata.

2. Water travels up through the xylem vessels from the roots to the leaves.

3. Increased temperature increases the rate of transpiration because water evaporates faster.

4. Increased wind speed increases the rate of transpiration by removing water vapour from around the leaf surface quickly.

Enzyme Action

1. The enzyme has an active site with a specific shape.

2. The substrate is complementary in shape to the active site, allowing them to fit together.

3. The substrate binds to the active site to form an enzyme-substrate complex.

4. The enzyme catalyzes the reaction and then releases the products, remaining unchanged.

Protein Structure & Synthesis

1. The sequence of bases in a gene (in the DNA) determines the sequence of amino acids in a protein.

2. mRNA carries a complementary copy of the genetic code from the DNA in the nucleus to a ribosome.

3. At the ribosome, amino acids are assembled into a chain in the specific order determined by the mRNA base sequence.

4. The amino acid chain then folds to create a specific 3D shape which determines the function of the protein.

Comparing blood vessels

Arteries have thicker muscular and elastic walls to withstand high-pressure blood pumped from the heart, whereas veins have thinner walls because they carry blood at a much lower pressure.

Veins contain valves to prevent the backflow of blood (as it flows under low pressure), while arteries have a narrower lumen to maintain this high pressure

Speciation

1. Isolation: Part of a population becomes isolated by an isolation barrier(geographical, ecological, or behavioural).

2. Mutation: Different mutations occur randomly in each of the separated sub-populations.

3. Natural Selection: Natural selection occurs, selecting for different mutations in each group due to different selection pressures.

4. Reproductive Isolation: Over many generations, the groups become so genetically different that they can no longer interbreed to produce fertile offspring

Natural Selection

1. Variation: Variation exists within a population due to random mutations.

2. Selection Pressure: An environmental pressure (e.g., predation, disease, lack of food) acts on the population.

3. Survival of the Fittest: Individuals with better-adapted characteristics (advantageous alleles) are more likely to survive and reproduce.

4. Inheritance/Evolution: These survivors pass their advantageous alleles to their offspring, increasing the frequency of these genes in the population over generations.

Photosynthesis

1. Light energy is trapped by chlorophyll (found in chloroplasts) and converted into chemical energy.

2. During the first stage (light reactions), water is split into hydrogen and oxygen.

3. Oxygen is released as a by-product, while ATP and hydrogen are passed to the second stage.

4. In the second stage (carbon fixation), hydrogen and carbon dioxide are used to produce sugar, facilitated by enzymes and ATP.