Key Area 1 Flashcards
What is the nucleus’s function?
The nucleus contains all genetic information for the cell to function and is in control of cell division.
What is genetic information stored in?
Long threads of DNA called chromosomes.
How do micro-organisms grow in number?
By cell division.
Why is cell division essential?
Cell division is essential to allow multicellular organisms to grow and repair by replacing damaged cells with new ones.
What are examples of the importance of cell division to multicellular organisms?
- Multicellular organisms use cell division to grow
- Multicellular organisms use cell division to repair damaged parts like cut or broken bones
What are chromosomes?
Chromosomes are thread like structures containing many genes stored in the nucleus of cells.
What do two single chromosomes make by joining by DNA replication?
Two identical sister chromatids (a double chromosome)
What is the chromosome complement?
The chromosome complement is the specific number of chromosomes each species has per cell.
What is the chromosome complement of a human?
Human chromosome complement = 46
How many sets of chromosomes do humans have?
Humans have 2 matching sets of chromosomes forming 23 matching pairs. In each pair, 1 chromosome came from the mother and the other came from the father.
How many sets of chromosomes does a diploid cell have?
Diploid cells have 2 matching sets of chromosomes (full chromosome complement - double genetic info)
How many sets of chromosomes does a haploid cell have?
Haploid cells have 1 set of chromosomes (half the chromosome complement)
What are examples of haploid cells?
The sex cells (sperm and egg in humans) are haploid to allow for the new offspring to have 2 matching sets of chromosomes (one set from sperm and one set from the egg).
All other cells are diploid.
Describe fertilisation.
Fertilisation takes place when the nucleus of the male haploid gamete (sperm) fuses with the nucleus of the female haploid gamete (egg) to form a diploid zygote, which divides to from an embryo.
How are more diploid cells produced?
More diploid cells are produced by a form of cell division called mitosis.
What is mitosis?
Mitosis provides new cells for growth and repair of damaged cells and maintains the diploid chromosome complement.
State what happens in the first stage of mitosis.
During this stage, the chromosomes copy themselves to form 2 chromatids. The chromosomes are difficult to see in the nucleus.
State what happens in the second stage of mitosis.
The chromosomes become easier to see as they shorten and thicken. The 2 chromatids are joined at a point called the centromere.
State what happens in the third stage of mitosis.
Towards the end of this phase, the membrane, surrounding the nucleus, disintegrates. Spindle fibres form and become attached to the chromosomes (each now 2 chromatids) at the centromeres. the chromosomes are arranged at the equator of the cell.
State what happens in the fourth stage of mitosis.
During this phase, the chromatids are pulled apart. The chromatids are now called chromosomes. The chromosomes move to opposite ends (poles) of the cell.
State what happens in the fifth stage of mitosis.
A nuclear membrane forms round each set of separated chromosomes and the cytoplasm and membrane divide.
State what happens in the sixth/last stage of mitosis.
Two identical daughter cells are formed.
How many chromosomes do the two identical daughter cells produced by cell division have?
The two identical daughter cells have the same number of chromosomes as the parent cell.
What are stem cells?
Stem cells are unspecialised cells found in all animals.
