Cells
The cell is the fundamental unit (building block) of all living organisms. May be one
simple cell (e.g. bacteria) or many complex and specialised cells (e.g. human).
In multi-cellular organisms:
Cells
Tissues
-
group of similar cells performing a particular function (e.g. muscles)
Organs
-
group of tissues performing a particular function (e.g. kidney, liver)
Systems
-
group of organs performing a function (e.g. circulatory system)
Whole organism
Typical Plant cell
(e.g. palisade cell)
µm = micrometer
1 millimetre = 1000µm
approximately 20 µm
cell wall
cell
membrane
chromosomes inside nucleus
large
central
vacuole
nucleus
mitochondria
40 µm
chloroplast
tonoplast
starch granules
cytoplasm
glycogen granules
nucleus
Animal cell
(e.g. cheek cell)
chromosomes inside nucleus
mitochondria
cell membrane
approximately 20µm
Differences between plant and animal cells
Plant
Animal
Cell wall
No Cell wall
Starch granules
Glycogen granules
Large central vacuole surrounded by
tonoplast
Occasional small temporary
vacuole only
May have chloroplasts
No chloroplasts
Functions
1.
Cell membrane
common to both. Controls what enters and leaves the
cell. Also holds cell in shape.
2.
Nucleus
common to both. Controls activity of cell. Contains
chromosomes, which are composed of DNA, which hold
instructions for the cell. Also is responsible for cell
division and replication.
3.
Mitochondria
Site for aerobic respiration – breakdown of food into
energy.
4.
Cytoplasm
Water based fluid where all chemical reactions occur.
5.
Glycogen granule
Carbohydrate in animal cell – food store.
6.
Cell wall
Plant cells only. Provides strength, support and gives
shape to cell. It is rigid, freely permeable (does not resist
anything coming in) and it contains cellulose.
7.
Chloroplast
Site for photosynthesis (to be discussed later)
8.
Starch granule
Plant cells only. Food store.
9.
Large central vacuole
contains water and regulates the water content of the
cell. If the cell is out of water, it supplies the water to
the cell.
10.
Tonoplast
membrane of vacuole.
Cell specialisation
Sometimes called differentiation.
Cells may be modified in their structure to carry out a particular function. This is called
specialisation or differentiation. For example, cells may be modified to become tissues
(e.g. muscles).
Specialist plant cells
1.
Palisade cell
-
found in upper part of leaf
absorbs sunlight
large number of chloroplasts
cells tightly packed together
2.
Root hair cell
-
same as normal plant cells, but has no chloroplasts, as it
is underground.
root hair increases surface area for absorption of water
and minerals.
-
Water moving into cell
Soil particles
Specialised animal cells
Sperm Cell
-
3 sections
tail to allow cell to move
acrosome with enzymes
it is a haploid – it has half the number of chromosomes
0.01mm
contains enzymes
tail
nucleus containing
chromosomes
Motor Neurone
nucleus
-
neurone means nerve cell
motor neurone takes electric impulses from the
brain/spinal cord (central nervous system) to a muscle
causing it to contract.
dendrites
axon
muscle
Impulse
nerve endings
myelin sheath
cytoplasm
Cell body
-
Intestinal cell
blood
long cells so that they can carry impulses around the
body quickly – faster reaction time.
dendrites connect to other neurons.
axon carries impulse along neuron to nerve endings.
myelin sheath insulates axon and so allows impulse to
travel quickly.
nerve endings transmit impulse to muscle making it
contract.
folds mean larger surface area for absorption of water
and nutrients.
water and nutrients are then passed on to the blood.
gut
nutrients
Cilia (in wind pipe) cell
-
hair are used to waft mucus down trachea (wind pipe)
Red blood cell
-
no nucleus means more space for haemoglobin (which
contains oxygen)
indent increases surface area
-
indent
side view