Download Pupil notes- sexual and asexual reproduction

Calderhead Highschool
S4 BIOLOGY
Unit 2:
Multicellular Organisms
2.1: Sexual and Asexual reproduction and
their importance
Learning Intention:
 2.1.1- Sexual and Asexual
reproduction and its importance for
survival
THE NEED TO REPRODUCE
All living organisms produce offspring through the process of reproduction.
There are 2 types of reproduction:
– Sexual reproduction
– Asexual reproduction
SEXUAL REPRODUCTION
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Most multicellular organisms use sexual reproduction to increase their
numbers
Sexual reproduction involves two parents (one male and one female) each
producing sex cells from their sex organs
Sexual reproduction produces offspring that resemble their parents but
are not identical to them.
REPRODUCTION IN PLANTS
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Flowering plants undergo sexual reproduction to produce seeds.
The sex organs of a plant are found inside the flowers.
They produce sex cells called gametes.
In flowering plants, male and female reproductive organs are found in the same
individual plant.
Male gametes are found in pollen grains which are produced in the anthers of
the flower.
Female gametes are found in ovules and produced in the ovary of the flower.
Fertilisation in plants is when the nucleus of the pollen grain fuses with the
nucleus of the ovule to form a zygote.
The gametes are haploid (has one set of chromosomes) and the zygote formed
from fusion of gametes is diploid (has two sets of chromosomes).
Label the flower diagram
The staMEN is the male part of the flower and is made up of the ANTHER and
FILAMENT
The ANTHER produces POLLEN grains
The FILLAMENT holds the anther in place
The stigMA is the FEMALE part of the plant. It is STICKY and catches pollen
grains
The OVARY contains the OVULES (the female sex cell).
Part of Flower
Ovary
Anther
Pollen
Stigma, Style and Ovary
Function
Female gamete
Makes pollen
Female reproductive organs
Why is sexual reproduction important?
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Sexual reproduction creates a variety of offspring
Variation is important because it create individuals with new combination
of genes
Different combinations may give useful characteristics such
as resistance to disease, tolerance to drought
The more variation there is in a population the more likely it is to be able
to survive changes in the environment.
* Task *
In your jotters, use your own words to summarise why sexual reproduction is
important- make sure to include examples
Flower Dissection
Method
• Collect two different flowers
• Carefully use the scalpal to dissect the flowers
• Use the labelled diagram from last time to help you identify each
structure
• Slice through the ovary and try to see the ovules
• Compare how different the structures are in each flower
• Stick the dissected flower parts into the space provided, label each
flower part and write the job it carries out
Task- in your jotters
• Write a paragraph comparing both flowers- their similarities and
differences
Plant reproduction
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There are two stages of plant reproduction:
- Pollination
- Fertilisation
Pollination
For fertilisation to occur, the sex cells must be transferred from the male
parts of the plant (the anther) to the female part of the plant (stigma). This
is done through the process of pollination.
There are two types of pollination: Self-pollination and Cross-pollination
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SELF-POLLINATION is the transfer of pollen from anther to stigma on
the SAME plant
CROSS-POLLINATION is the transfer of pollen from anther to stigma
on DIFFERENT plant
Pollination is either carried out by the wind or by insects. Insect and wind
pollinated plants have different structures to suit the way they are pollinated.
Insect pollination
Plants which need insects to carry pollen from the anther to the stigma (insect
pollinated plants) have SCENTED, BRIGHTLY COLOURED PETALS and store a
sweet NECTAR in order to attract insects. Their pollen grains are SPIKED so
that they stick to insect’s hairs when they visit the flower.
Wind Pollination
Wind pollinated plants do not need to attract insects. They don’t have bright
petals and they don’t produce nectar. Instead the anthers and stigma hang
loosely out of the flower. This means the light smooth pollen is easily blown
from the anthers and the feathery stigma are able to catch the pollen grains
carried in the wind.
Complete the table comparing wind and insect pollinated plants:
Fertilisation
When a pollen grain reaches the
stigma, a pollen tube forms from
the grain and grows down towards
the ovary. When fully formed it
transports the male gamete from
the pollen grain to the female
gametes in the ovule where they
fuse and fertilisation occurs.
The OVARY becomes the FRUIT and OVULES become the SEEDS.
PETALS then die and drop off
Animal Reproduction
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Almost all animals reproduce through sexual reproduction which involves
sex cells (gametes)
In humans the male sex cell is the sperm and the female sex cell is the
egg
Fertilisation will occur when the nucleus of the sperm cell fuses with the
nucleus of the egg cell, forming a zygote.
In humans, fertilisation happens in the oviduct (aka fallopian tube)
Both male and females have different reproductive organs which have
different jobs.
HUMAN REPRODUCTIVE SYSTEMS
Structure
Function
Deposits sperm in the female
Testes
Sperm duct (vas deferens)
Males are continuously fertile which means that they are constantly producing
millions of sperm cells.
Structure
Function
Oviduct
Ovary
Fertilised egg implants into lining and
foetus develops here
Receives sperm from the male
Female humans have cyclical fertility, meaning that they are only fertile at
specific times. Human females only release one egg every month and are only
fertile for 2-4 days.
A spike in hormone levels triggers the release of a female’s egg cell and it
travels down the oviduct by being brushed along by tiny hairs called cilia.
If the egg cell meets a sperm cells and fertilisation occurs, a zygote is formed
and implants in the uterus lining and develop into a foetus.
http://www.bbc.co.uk/education/clips/zsrg9j6 (useful video)
Fertilisation
There are two types of fertilisation:
- Internal fertilisation
- External fertilisation
External fertilisation
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Most animals that live in water carry out external fertilisation. This is
when the sperm and egg cells are released into their surrounding
environment; they meet and fuse OUTSIDE the body. Large numbers of
the sex cells are released due to the risk of eggs being eaten by
predators or cells drifting away before they are fertilised.
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Unfertilised gametes make up part of sea plankton (and become part of
aquatic food chains)
In fish such as trout, once the fertilised eggs develop, they hatch. There
is no parental care for the newly hatched young and so the fish must use
their yolk sac as a food source until they are able to swim and feed on
their own.
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Internal fertilisation
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The majority of land animals carry out internal fertilisation. Internal
fertilisation is complicated because:
- Mates need to find each other (and compete with rivals)
- Mating needs to be co-ordinated with seasonal timing of gamete production
-Specialised reproductive organs are needed
-Parental care is needed after the young are born
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For fertilisation to take place internally, the sperm cell is placed inside
the body of the female during sexual intercourse. This method has an
increased chance of fertilisation because the gametes have been placed
close together.
TASK
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Write a paragraph comparing internal and external fertilisation
Asexual Reproduction
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In single celled animals, cell division occurs to allow them to reproduce.
Two identical cells are formed.
This type of reproduction is called asexual reproduction and it involves
only one parent.
All offspring produced this way are genetically identical and known as
clones.
Examples
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Single celled organisms (such as amoeba) grow by BINARY FISSION.
This is when the parent cell divides into two identical daughter cells.
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Yeast cells increase their numbers through BUDDING. The new organism
forms a bud which then breaks off from the parent then continues to
grow.
Multicellular organisms such as plants can reproduce sexually (with flowers) or
asexually (without flowers)
• Plants which reproduce asexually produce structures to help them. The
structures include:
– Runners
– Tubers
– Bulbs
Learning Outcomes
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the topic.
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2.1 Learning Outcomes – National 4 – Sexual and Asexual Reproduction
1. Reproduction is
_______________________________________________________________
2.
How many parents does each form of reproduction involve?
Sexual - _____ parents
Asexual - _____ parent
3.
Asexual reproduction leads to genetically ______________
offspring, known as ____________ and makes species less well
________________.
4.
Sexual reproduction involves _________ cells and leads to
____________ in offspring.
5.
State which part of flowering plants contains which gamete.
Pollen contains ____________ gamete.
Ovule contains ____________ gamete.
6. State the function of the different parts of the flower.
Stamen –
Anther –
Stigma –
Ovary –
Ovules –
Face
7. Pollination is the transfer of ____________ from the __________ to the
__________ and can occur by __________ or __________.
8.
State the features of wind pollinated flowers.
9.
State the features of insect pollinated flowers.
10. Describe the role of the growth of a pollen tube in fertilisation.
11. Sexual reproduction can be _______________ or ______________.
Sexual reproduction in ______________ is internal and involves the sex
cells known as __________ in females and __________ in
males.
12. Describe the main features of sperm.
13. Describe the main features of eggs.
14. State where the sex cells are produced.
Sperm –
Eggs 15. Describe the process of fertilisation in mammals.
16. Describe what happens to an egg cell after fertilisation.
17. State the importance of internal fertilisation to land-living animals.
18. Describe the method of external fertilisation as used by fish.
19. State the stages in the development of the embryo fish.
20. Explain the relationship between the number of eggs and chances of
survival. Relate this to parent care.