cell division exam questions Flashcards
(14 cards)
Explain how DNA is replicated in the lagging strand giving refence to the direction that replication occurs.(3 marks)
DNA polymerase synthesizes new DNA 5’ to 3’. The lagging strand’s templates is wound around DNA polymerase or it would be in the wrong orientation. The lagging strand is synthesizes in okazaki fragments.
The naked mole rat is a mammal that is
extremely resistant to cancer.
Suggest, with reasons, which parts of the cell cycle naked mole rats might have special mechanisms for.(3)
-DNA replication and Mitosis
-mutations can occur during DNA replication when DNA polymerase makes mistakes
-And when DNA is exposed to reactions in the cytoplasm.
Why are mutations more likely to occur in the S phase than the G1 phase?(2)
-S phases more prone to mistakes as they can add/substitute/delete bases while copying DNA
-DNA is transcribes to RNA
Describe the role of movement of water in the opening and closing of stomata in the leaves. (3)
Water moves into the cell by osmosis to open the stomata: it causes the cell to bend due to their thicker inner walls so they form a pore with increasing turgidity. Water leaves the cell by osmosis the guard cells become flaccid and the pore begins to close.
Describe the process of differentiation.
-Differentiation is the process of which stem cells become specialised.
-The number and type or organelles within a cell changes.
-Fully differentiated cells are unable to divide by mitosis
-driven by changes in gene expression
-differentiated cell can only express a subset of their genes
stem cell can express all their genes in the genome.
Explain the advantages of stem cell transplants than traditional inter individual transplants.
-Stem cells are derived from patients own stem cells.
-Will not contain foreign antigens and not be rejected by their immune system- no immunosuppressant drugs.
-Stem cells can be reprogrammed to form tissues required- no waiting list of donors.
Outline arguments against embryonic stem cells for medical research.
-Embryos have the potential to become humans but are destroyed by stem cell research
-Donor Embryos can be rejected for growing transplanted tissue as they have different antigens to the recipient.
Explain why plants are able to store large quantities of starch without reaching maximum capacity.
Max turgidity occurs when water moves into a cell by osmosis, as the inside of the cell has a lower water potential than the outside of the cell. As starch is insoluble it does not effect the water potential. so osmosis in the cell is avoided.
What is meant by the term homologous chromosomes?
A pair of chromosomes in which each chromosome contains the same genes.
Why would a parallel flow gas exchange system be less efficient than a counter current gas exchange system?
-In a parallel flow system, the oxygen concentration gradient between water and blood decreases with distance along the gill
-Rate of oxygen diffusion will decrease.
-Less oxygen diffuses into the blood than the CCS where the concentration gradient is maintained.
How does a grasshopper pump air in and out of its body?
It changes the volume of its body with rhythmic abdominal movements which changes the pressure in its body so that air id drawn in and out through spiracles.
Explain how changes in the buccal cavity of a bony fish allows the gills to be ventilated?
When the fishes mouth open, the floor of the buccal cavity is lowered increasing the cavity’s volume. This decreases the pressure. so water is drawn into it. When the mouth closes, the floor is raised this decreases the volume and increases the pressure in the cavity so water is forced out across the gill filaments.
Why is it not possible to expel all air from your lungs?
-the thorax can not be completely compressed
-trachea is held open by cartilage
-bronchioles/ alveoli are held open by elastic fibres.
Outline how vesicles are moved from one organelle to another.
Microtubules proves a pathway for movement. The vesicles moves along the microtubules.
The microtubules are then broken down
-uses ATP
