Slides in this set
What is Meiosis?
Cell devision that halves the number of chromosomes to produce gamets.
The four new cells are genetically different from each other and from the
As meiosis begins, the chromosomes start to become visible. At this stage they have produced replicas of each
other. The centrioles separate and move to opposite poles (ends) of the cell.
· The chromosomes shorten and fatten and become clearly visible. Similar-looking, or homologous, chromosomes
line up alongside each other in pairs. Each pair of matching chromosomes is called a bivalent.
· Each chromosome is now seen to consist of two threads. These threads are called chromatids and each is an
exact copy of the parent chromosome. The chromatids are joined together at a point called the centromere.
· The paired chromosome (bivalents) migrate to the middle line, or equator, of the cell. The nuclear membrane
disappears. From the centrioles, a system of fibres called the spindle, stretches across the cell.
· The chromosomes separate from their homologous partners and move to opposite poles of the cell. Each side of
the cell now contains just half the normal number of chromosomes.
· Nuclear membranes form and the cell splits into two. The centrioles duplicate and move to the poles of the
daughter cells. New spindles begin to form. In many species, complete division does not occur at this stage.
· New spindles have formed and the nuclear membranes have disappeared. The chromosomes, each consisting of
two chromatids joined together at the centromere, migrate to the equators of the daughter cells.
· Each chromatid separates from its partner and they move to opposite poles of the cell. These chromatids are now
really daughter chromosomes and the ends of each cells have the haploid number (n=3).
· Nuclear membranes form round the chromosomes and each cell splits. So, a diploid (2n=6) mother cell has now
been converted into four haploid (n=3) gametes.…read more
What is Mitosis?
Cell devision that makes two new cells identical to each other and to the
· Between divisions, a copy of each chromosome is made. The chromosomes then start to become
visible. The centrioles separate and move to opposite poles (ends) of the cell. The chromosomes
are clearly visible. They each consist of two threads called chromatids, each an exact copy of the
parent chromosome. Chromatids are joined together at a point called the centromere.
· The nuclear membrane disappears. The paired chromatids migrate to the middle line or equator,
of the cell. From the centrioles, a system of fibres called the spindle stretches across the cell.
· Each chromatid separates from its partner and they move to opposite poles of the cell (the spindle
is thought to be involved in this). The chromatids are now considered to be daughter
· Each half of the cell now has the correct number of chromosomes (six for this species). New
nuclear membranes form around them and the cytoplasm starts to divide.
· Cell division is complete. The chromosomes are no longer visible. Two daughter cells have been
formed whose nuclei contain six chromosomes identical to the original six of the parent cell.…read more
· Movement Animals move to find food and away from predators and plants move
· Reproduction Both animals and plants reproduce to keep their species in existence.
· Sensitivity Animals and plants are sensitive to their surroundings due to their
· Nutrition Animals need food for respiration and plants need minerals from the soil.
· Excretion Waste products must be excreted from plants and animals.
· Respiration Animals and plants must turn their food into energy by respiration.
· Growth Animals grow larger and stronger which helps them hunt better.…read more
Classification of Living Things
· GCSE Biology > Classification of Living Things
Living things are grouped into 1 of 5 kingdoms which are as follows: Animals, Plants,
Fungi, Protista, and Monera. The list below shows the other attributes (in order) which
are used to more accurately classify living things, down from their kingdom to their
Cells / Tissues / Organs
· This section lists pretty much everything to do with living cells, which includes tissues and organs. Have fun revising
everything below!!! Protoplasm Consists of cytoplasm and nucleus. Cytoplasm Jelly like substance where chemical
reactions take place and other parts are embedded. Nucleus Controls reproduction and also contains the characteristics
of the cell. Cell membrane Surrounds the cell and controls what moves in and out of the cell. Mitochondria Found only
in plant cells where respiration occurs. Chloroplasts These makes plants green. They contain chlorophyll which is
needed for photosynthesis. Cell wall Gives the cell its shape. The cell's "skeleton". Vacuoles Where the cell sap is
· The differences between animal and plant cells are as follows: Plant cells have:
Chlorophyll in chloroplasts,
A cellulose cell wall,
· Animal cells have:
No Chlorophyll or chloroplasts,
No Cellulose cell wall,
Small or no vacuoles.
· Tissues are made up of lots of cells of the same type. (e.g. muscle tissue is made up of many muscle cells)
· Organs are different tissues working together to carry out a certain function. An organ can contain different types of
tissue (e.g. the heart)…read more