Maintenance of Organisms Flashcards
what is mitosis and when does it occur
mitosis is a type of cell division
occurs wherever more cells are needed
produces two new cells that are identical to each other, and to the parent cell
the process of growth and division is called the cell cycle.
four functions of mitosis
- Growth of an organism: An adult human being is made up of billions of cells and all cells have the same genetic material. This genetic stability is achieved by mitosis.
- Repair: In the case of wound healing cells should be replaced with the same type of cells with the same genetic quality.
- Replacement
- Asexual reproduction: Asexual reproduction occurs in single-celled organisms, but also in plants and other organisms.
where does mitosis occur in plants
In plants, mitosis occurs in growing areas called meristems.
There is a meristem at the end of every shoot and every root and in a thin layer around the stems of woody plants, between the new xylem on the inside and new phloem on the outside.
where does mitosis occur in insects
Insects have an exoskeleton, so before it can grow the old skeleton must be cast off.
Most insects moult a number of times during their life.
Mitosis occurs in the layers immediately beneath the skeleton and in other organs where growth is occurring.
where does mitosis occur in mammals
Bones are essentially non-living so growth tends to occur mostly at the end of long bones in an area called the growth plate.
Cells which need constant renewal such as red blood cells and skin cells are constantly replaced via mitosis.
what is cytokinesis
Cytokinesis is the process in which the cell actually divides into two.
With the two nuclei already at opposite poles of the cell, the cell cytoplasm separates, and the cell pinches in the middle, ultimately leading to cleavage.
importance of cytokinesis
– ensures that chromosome numbers remain constant
– after mitosis, 2 sets of chromosomes are made, so cytokinesis ensures that two cells with the normal amount of chromosomes are made
cytokinesis in animals
Occurs during a process called cleavage
A ring of microfilaments constricts the centre of the cell until it splits
cytokinesis in plants
The dividing plate - or cell plate - forms across the centre of the cell
This splits the cell into two new cells
The cell plate forms the new cell wall
Stages of mitosis
P - Prophase (Phase one)
M - Metaphase (middle)
A - Anaphase (away)
T - Telophase (two)
Prophase -> phase one -> chromosomes condense and the nuclear membrane breaks down.
Metaphase -> middle -> chromosomes line up in the middle (spindle fibres co-ordinate this)
Anaphase -> away -> chromosomes move towards opposite poles of the cell (they look like little sideways ‘A’s when they do this)
Telophase -> two -> The spindle disappears. Two new nuclear membranes appear.
what is the endosymbiotic theory
describes how a large host cell and ingested bacteria could easily become dependent on one another for survival, resulting in a permanent relationship
Over millions of years of evolution, mitochondria and chloroplasts have become more specialized and today they cannot live outside the cell
similarities mitochondria and chloroplasts have with bacteria
they have their own DNA, which is separate from the DNA found in the nucleus of the cell.
both organelles use their DNA to produce many proteins and enzymes required for their function.
a double membrane surrounds both mitochondria and chloroplasts, further evidence that each was ingested by a primitive host.
The two organelles also reproduce like bacteria, replicating their own DNA and directing their own division.
