1. 1.4 Cells
Cell structure
An organism is made-up of cell. Organelles: components arranged in a special way,
and carries out a particular job.
1) The cell membrane surrounds the cell. It is very thin and cannot be seen
using a light microscope. It holds the substances in the cell.
2) Inside the cell-membrane is a soup of chemicals and complex structures which
carry out all of the activities of the cell. It is called the cytoplasm.
organelles, specialised areas of the cell where particular jobs are carried out.
3)The granules can also be small vesicles which store food reserves or break down
unwanted substance. The cytoplasm is colourless but the consistency can vary
from a thick gel to runny.
4)Each cell has a nucleus, to control the activities of the cell. it stores all the
information in coded form in molecules of DNA (deoxyribonucleic acid) found in the
chromosomes.
Plant cells
1. The cell wall is made by the plant cell from a special chemical called cellulose.
This chemical has long fibers and is very strong. It forms a wall on the outside
of the cell membrane to support the cell and stop the contents bursting when it
is full of water.
2. The permanent vacuole is a bag-like structure containing a dilute solution. It
is seen in the middle of the cytoplasm. Its functions include the storage of
waste substances, or giving colour to the cells e.g. the red of beetroot.
3. Chloroplasts are the structures that contain the green pigment chlorophyll.
They are not found in every plant cell but there are many in leaf cells. They are
seen as small green dots in the cytoplasm of the cells. They trap light energy to
make food for the plant. They are separate from the cytoplasm by membrane
but chemicals can move between the two very easily.
See pg.16(the table)
Unicellular organisms
They are multicellular unicellular. Some unicellular organisms have a nucleus
surrounded by a nuclear membrane (like the nucleus in an animal or plant cell).
See table pg 17.
Summary
O Organisms are made up ofcells.
O The cell membrane controls which chemicals enter or leave the cell.
O The nucleus contains the coded information to control the cell. It contains chromosomes of
DNA,
O The cytoplasm is where reactions take place in the cell.
O Animal cells do not have cell walls,permanentvacuoles or chloroplasts butplantcells do.
O Bacteria do not have a nucleus butthe information is in a circular chromosome ofDNA.