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science world 1 – chapter 7
cells (& reproduction)
CELLS
All organisms (i.e. living things) are made of cells. Your body
contains over 3 billion cells that are so small they can only be
seen by a microscope. Some cells can be seen with your naked
eye e.g. birds’ eggs are single cells.
Some organisms consist of only one cell and they can live
completely independently from other organisms. However,
large organisms contain many different types of cells and each
type of cell is specialised. This means that each type of cell has
a different job to do in the organism. For example, in the human
body, red blood cells carry oxygen around the body.
CELLS IN ORGANISMS
There are three main parts in every cell (both plant and animal)
that can be clearly seen using a light microscope:
Cell membrane – the thin layer that surrounds each cell. It
gives the cell its shape and controls what
enters and leaves the cell.
Nucleus – the control centre (brain) of the cell. It controls all
the cell’s activities, and without it the cell will die.
Cytoplasm – the jelly-like liquid that fills up most of the space
in the cell. This is where many chemical reactions
take place. It also contains many other structures
called organelles that helps the cell to function
properly.
Plant cells contain some parts that animal cells don’t have.
These include:
Cell wall – a thick, tough layer on the outside of the cell
membrane that protects the softer parts inside the
cell. It also helps support the plant.
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Vacuoles – large liquid-filled spaces where dissolved
substances and water are stored. Some animal cells
may have small vacuoles, but most have none at all.
Chloroplasts – organelles found in the cytoplasm of plant cells.
They contain the green pigment chlorophyll,
which is needed for photosynthesis.
CELLS, TISSUES & ORGANS
Living things that are made up of many different types of cells
are called multicellular organisms. Different cells have certain
jobs to do - we say that those cells are specialised. They need to
work together with the other cells for the survival of the
organism.
Tissues – These are similar cells working together in groups to
do a particular job e.g. muscle tissue, nerve tissue,
skin tissue.
Organs – These are made up of different tissues working
together to perform a particular function. For
example, the stomach contains muscle tissue, gland
tissue and connective tissue that all work together to
help digest (break down) food.
SPELLING WORDS
EASY
1 cells
2 light
3 body
4 plants
5 animals
6 living
7 waste
8 muscle
9 gases
10 brain
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12
13
14
15
16
17
18
19
20
EASY
lens
focus
eyepiece
stage
mirror
genes
nerve
blood
digest
organ
HARD
1 microscope
2 structures
3 organism
4 chloroplast
5 tissues
6 specialised
7 organelles
8 function
9 nutrients
10 muscle
2
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12
13
14
15
16
17
18
19
20
HARD
oxygen
objective
diaphragm
membrane
nucleus
multi-cellular
cytoplasm
connective
vacuoles
photosynthesis