S1 Science: Section 4
Microscopes, Cells and Reproduction Summary
Microscopes
Microscopes are used to look at objects (specimens) which are too small to
see with our eyes. To look at the specimen under the microscope you must
place it on a small piece of glass called a slide.
Eyepiece
Stage clips
Objective lens
Slide
Stage
Focussing knobs
Mirror
Part
Eyepiece
Objective
lens
Stage
Mirror
Stage Clips
Function
To look through
To magnify object
To place slide on
To direct light
through the object
To hold slide in place
When using a microscope you should
 never use the sun as a source of light as this can seriously damage
your eyes
 ensure the specimen is thin to allow light to pass through
 cover the specimen with a coverslip to keep it flat
 add a stain to the specimen to make it easier to see
 always look at a slide using the low power objective lens first
Cells
Cells are the basic unit of all living things. Some living things, such as
bacteria, consist of only one cell. Other living things, including humans, are
multicellular (are made of lots of cells).
Cell wall: rigid boundary of plant cells which
helps give cell its’ shape
Cell membrane: controls the
substances which enter and leave
the cell
Nucleus: the control
centre of the cell
Chloroplasts: help plant to trap sunlight to
make food
Cytoplasm: site of chemical
reactions
Vacuole: storage of water
Animal cell.
Plant cell.
Section 4: Microscopes, Cells and Reproduction: Summary
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Reproduction
Sexual Reproduction in Humans
Reproduction is the process by which new living things are produced to
replace those which die from disease, old age or are eaten by predators.
Many animals (including humans) and plants reproduce by sexual
reproduction.
Oviduct
Uterus (womb)
Ovary
Vagina
Sperm
duct
Testes
Penis
Sexual reproduction requires sex cells. Female animals produce eggs from
the ovaries, male animals produce sperm from the testes.
Egg cell
Sperm cell
sperm about to enter the ovum
.
To make a new individual, a male and female sex cell must fuse (join)
together. This is called fertilisation. In humans fertilisation occurs in the
oviduct (egg tube).
Each month an ovary
releases an egg cell
into an oviduct.
The sperm cells swim
through the uterus
to the oviduct.
If they meet an egg The fertilised egg
cell, fertilisation will cell divides into a ball
occur.
of cells (an embryo).
The embryo travels
down the oviduct and
implants into the
uterus lining.
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Pregnancy and risks to the embryo
Once the embryo has implanted the woman is pregnant. During this time
the placenta and umbilical cord supply the developing baby with oxygen and
food. The baby is carried in a fluid filled bag called the amniotic sac.
placenta
amniotic sac
waste materials out
(e.g. carbon dioxide)
amniotic fluid to
protect the foetus
foetus
food and
oxygen
in
umbilical
cord
mother's
blood
 Ultrasound scans are used during pregnancy to check whether or not
the baby is developing normally and measure its size.
 During pregnancy the mother should avoid smoking, taking drugs and
drinking excess alcohol.
In vitro fertilisation (IVF)
For many reasons some couples have difficulty conceiving a baby. In vitro
fertilisation (IVF) can help these couples.
 IVF involves removing sperm and eggs from the parents and mixing
them together in the laboratory
 If an egg is successfully fertilised it can be put into the mother’s
uterus where it will hopefully result in a pregnancy.
 IVF is expensive and doesn’t always result in a pregnancy.
Inheritance
Children share features with their mothers and fathers but do not look
exactly like either parent.
 The child inherits genetic information from both parents.
 Humans all look different from one another because
we all carry different genetic information.
Genetic information is stored in the cell nucleus in structures called
chromosomes.
 The chromosomes are made of a chemical called DNA.
 Each chromosome contains many genes.
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 Each gene controls a different feature of an individual e.g. eye colour
or hair colour.
Cell division
New cells are made by cell division and are required for growth and repair.
The new cells (often called daughter cells) contain exact copies of the
genetic information found in the parent cell.
New cells are required for growth (e.g. embryo to baby or child to adult)
and also for repair e.g. skin damaged by a burn or fall.
Stem cells are cells which have not yet specialised to become a particular
cell type e.g. nerve cell.
 Once a cell is specialised, it may not be able to divide and make new
cells when required.
 Scientists are hoping to work out how to tell a stem cell to specialise
into different cell types to help treat diseases e.g. Parkinson’s
disease
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Types of reproduction
There are two types of reproduction: asexual and sexual.
Asexual
Sexual
Asexual reproduction
 one parent dividing in two to give new individuals.
 is much quicker than sexual reproduction
 produces individuals which are identical to the parent. This can be a
disadvantage as all individuals have the same weaknesses e.g. prone to
the same illnesses.
Sexual reproduction
 involves two parents (one male, one female) producing sex cells which
join together to make a new individual
 takes much longer than asexual reproduction
 produces individuals which are different from one another
Development in Other Animals
Some young are very different from their parents. Metamorphosis is a
complicated process that some animals undergo when they change from
juveniles to adults.
Caterpillar
pupa
or larva
Adult
butterfly
Examples of animals that undergo this process are frogs, toads, midges,
moths and butterflies.
Section 4: Microscopes, Cells and Reproduction: Summary
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