D2.1 - Cell and nuclear division Flashcards
Why do all organisms need to produce new cells?
For growth, maintenance and reproduction.
How do cells produce new cells?
Through cell division.
What is cell division in simple terms?
When one cell divides into two.
What is a mother cell?
The cell that divides.
What are the daughter cells?
The cells that are produced from the mother cell.
What happens to the mother cell during cell division?
It disappears as a whole in the process, unlike reproduction by animal parents.
What is a theory that has strong evidence behind it in terms of when new cells are produced?
There is strong evidence for the theory that new cells are only ever produced by division of a pre-existing cell.
What evidence is there for the theory that new cells are only ever produced by division of a pre-existing cell
If we consider the trillions of cells in our bodies, each one was formed when a pre-existing cell divided in two. We can trace this back to the original cell, which is the zygote. The zygote was the start of our individual lives, was produced by the fusion of a sperm and egg.
Sperm and egg cells were produced by cell division in our parents. The origins of all cells in our parents’ bodies goes back to the zygote from which they developed and then on through all previous generations of human ancestors. If we accept that humans evolved from pre-existing ancestral species, we can trace the origins of cells back through hundreds of millions of years to the earliest cells on Earth. This means there is a continuity of life from its beginnings to the cells in our bodies today.
What happens in cytokinesis?
The cytoplasm of a cell is divided between two daughter cells.
What is cytokinesis apart of?
Cytokinesis is a part of cell division, along with nuclear division by mitosis or meiosis.
When can the process of cytokinesis begin?
As soon as chromosomes have separated and are far enough apart to ensure that none of them end up in the wrong cell.
What does cytokinesis do?
All the cytoplasm and its contents of the mother cell are shared out between the daughter cells.
What is one difference between plant and animal cells?
They carry out cytokinesis differently.
Explain how cytokinesis occurs in animal cells?
In animal cells, the plasma membrane is pulled inwards around the equator of the cell to form a cleavage furrow. This is accomplished using a ring of contractile proteins immediately inside the plasma membrane, usually at the equator. The contractile proteins are actin and myosin and are similar to those that cause contraction in muscle. When the cleavage furrow reaches the centre, the cell is pinches apart into 2 daughter cells.
Explain how cytokinesis occurs in plant cells?
In plant cells, microtubules are built into a scaffold straddling the equator, which is used to assemble a layer of vesicles. The vesicles fuse together to form plate-shaped structures. With the fusion of more vesicles, two complete layers of membrane are formed across the whole of the equator of the cell. They become the plasma membranes of the 2 daughter cells adjacent to the new dividing walls. they are connected to the existing plasma membranes at the sides of cell, completing the division of the cytoplasm.
What is the stage that occurs in plants after cytokinesis?
The next stage in plants is for pectins and other substances to be brought in vesicles and deposited by exocytosis between the 2 new membranes. this forms the middle lamella that will link to the new cell walls. Both daughter cells then bring cellulose to the equator and deposit it by exocytosis adjacent to the middle lamella. As a result, each cell builds its own cell wall across the equator.
What does cytokinesis generally do?
In many cases, cytokinesis divides the cytoplasm of the mother cell into equal halves.
How do cells split equally?
This happens in a growing root tip. Root growth is due to enlargement and division of cells arranged in columns. The cells in a column all differentiate in the same way, so cytoplasm is apportioned equally when they divide.
Why can unequal division occur?
Cytoplasm is sometimes divides unequally. Small cells produced by unequal division can survive and grow if they recieve a nucelus and at least one of each organelle that cannot be assembles from components in the cell.
3 examples of unequal division
For example, mitochondria can only be produced by division of a pre-existing mitochondrion, so there must be at least one mitochondrion in a daughter cell for it to be viable. Another example of unequal division are budding in yeast and oogenesis in humans.
What is budding?
Yeast cells reproduce asexually, and this process in called budding.
Explain budding in yeast
The nucleus divides by mitosis. A small outgrowth of the mother cell is formed. It receives one of the nuclei, but only a small share of the cytoplasm. A dividing wall is constructed, separating the 2 cells. The small cell then splits away, leaving a scar where it was attached to the larger cell. Yeast cells carry out this budding process repeatedly and do not have to double in size between each division.
How are sperm and eggs produced in humans?
The production of both sperm and eggs in humans starts with 2 division of a mother cell.
