SB2 revision Flashcards
How many pairs of chromosomes are present in a diploid nerve cell?
23
What happens immediately before mitosis in the cell cycle?
Checking for errors in the duplicated DNA
What phase in mitosis involves the pulling of chromosomes and their copies to different ends of the cell?
Anaphase- The spindle fibres pull the chromosomes apart, leaving 2 chromatids on each side of the cell.
Explain the difference between sensory, relay and motor neurones, in terms of the direction that their electrical signals travel
Sensory neurones send electrical impulses to the CNS
Relay neurones send electrical impulses to the the brain and spinal cord.
Motor neurones send electrical impulses away from the CNS and to effectors like muscles.
Explain why reflex arc signals do not immediately go to the brain.
It would take longer to react if it did therefore increasing the amount of damage on the body.
Describe how embryonic and adult stem cells are different?
Embryonic stem cells can differentiate into any possible cell type whereas adult stem cells can only differentiate into specific stem cells depending on where they were. e.g an adult stem cell in the blood can only differentiate into a blood cell.
State what types of human cells are not produced by mitosis?
Gametes.
Describe how someone with short sight can see more clearly?
They could use a concave lens to help refract light onto the retina instead of before it.
Explain the process of accommodation
The process of the lens changing shape to see a near or distant object.
The lens thickens to allow light to refract more strongly onto to the retina in order to view nearer objects.
The lens gets thinner to allow light to refractn slightly onto the retina in order to focus on distant objects.
Describe the interphase stage of mitosis
All DNA and organelles in the cell are duplicated and the cell grows.
Describe the prophase stage of mitosis
The chromosomes condense getting shorter and fatter. The nuclear membrane breaks down and the chromosomes roam free in the cytoplasm. Spindle fibres form around the cell.
Describe the metaphase stage of mitosis
The chromosomes line up in the centre of the cell.
Describe the anaphase stage of mitosis
Spindle fibres pull the chromosomes to each end of the cell, splitting up the pair. The chromatids are on opposite ends of the cell.
Describe the telophase stage of mitosis
New nuclear membranes form around each of the sets of chromosomes. There are temporarily 2 nuclei in the cell.
Describe the cytokinesis stage of mitosis
The cytoplasm and cell membrane of the cell divides, leaving 2 genetically identical daughter cells.
number of cells =
2 to the power of n/ 2^n
What is the process of elongation?
a plant cell expands making the cell bigger and so the plant grows.
Name a process that is used for growth in plants but not animals.
Cell elongation.
Describe how a plant grows by cell elongation?
The plant grows continuously as the cells continue to expand so the cells grow bigger.
Why is cell differentiation important for the development of specialised cells?
Because they allow cells to develop different functions so that different parts of the body can function.
