Post on 23-Aug-2018
2.1. Sexual & asexual reproduction & their
importance for the survival of species
2.2. Propagating & growing plants
2.3. Commercial uses of plants
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2.1 Sexual and asexual reproduction and their
importance for the survival of species. Covered
() How well can you
do this?
1. I can state that reproduction increases the number of organisms in
a population and is essential for the survival of a species
?
2. I can state that sexual reproduction involves two parents and
produces genetically different offspring
?
3. I can state that asexual reproduction involves one parent and
produces genetically identical offspring called clones
?
4. I can give examples of the type of reproduction carried out by
named organisms
?
5. I can define fertilisation as the fusion of the nuclei from the male
and female sex cells
?
6. I can explain the difference between internal and external
fertilisation and state the advantages and disadvantages of each
?
7. I can explain the relationship between the number of sex cells
produced and the success rate of fertilisation
?
8. I can state that there are different degrees of protection
offered by parents to their young and give examples
?
9. I can calculate the percentage survival of organisms. ?
2.2 Propagating and Growing Plants Covered
() How well can
you do this?
1. I can state that propagation is a process by which a grower
increases the supply of a type of plant
?
2. I can state that there are different methods used to
propagate plants
?
3. I can state that plants can be grown from seeds and I can give
some examples
?
4. I can describe seeds as coming in different shapes and sizes ?
5. I can explain that large seeds can be sown individually and small
seeds are mixed with silver sand before sowing
?
6. I can explain that seeds are formed sexually from male and female
sex cells, and so plants that develop from seeds are not all identical
?
7. I can state that some plants can be propagated from bulbs and
tubers and I can give examples
?
8. I can state that some plants produce miniature plants called
plantlets attached to the parent.
?
9. I can give examples of plants that can be grown from
structures called runners and offsets
?
10. I can state that plants can be propagated by artificial
methods and these methods include cuttings or layering
of a parent plant
?
11. I can state that a propagator may be used to encourage the
growth of plant cuttings
?
12. I can state that the use of protected cultivation includes the use
of greenhouses and polythene tunnels
?
13. I can describe the effect on plant growth of adding additional
carbon dioxide, heat or light in protected cultivation
?
2.3. Commercial uses of plants Covered
() How well can you
do this?
1. I can state that plants are grown to produce food ?
2. I can state that plants are used to produce food and raw materials
and are grown to make medicines and fuels
?
3. I can describe that the demand for food is increasing as the
world’s population increases.
?
4. I can explain that plant yields can be increased using pharming
techniques.
?
5. I can describe that pharming techniques involve removing genes
from one species and inserting them into a plant species.
?
6. I can state that inserting new genes into a plant species can make
new products or cause an increase in crop yield
?
7. I can give examples of how pharming techniques improve plants ?
8. I can explain why genetically modified (GM) crops might have a
negative impact on the environment
?
2.1. Sexual and Asexual Reproduction and their importance for the survival
of species
Reproduction
All living things must reproduce in order to produce offspring similar to themselves. This is
essential for their survival. If they were unable to reproduce they would decrease in
number and become extinct.
Sexual Reproduction
Most multicellular organisms use sexual reproduction as a means of increasing their
numbers. This involves two parents, male and female, each producing sex cells called
gametes. Sexual reproduction increases the variety in a species.
In animals the male gametes are called sperm and are produced in the testes. The female
gametes are called eggs and are produced in the ovaries.
Sperm cells
Egg cell
Sperm cells produced
by the testes
Egg cells produced
by the ovaries
In plants sexual reproduction results in the production of seeds which develop into new
plants.
The male sex cells in plants are called pollen grains and produced by the anthers and the
female gametes are called ovules and produced by the ovary.
Name of Part Function
Food Store Provides material and energy for
growth of new plant
Embryo Grows into a new plant
Seed Coat Protects the seed
Anther produces
pollen grains
(male sex cells)
Ovary produces
ovules (female sex
cells)
Embryo
Seed Coat
Food Store
Asexual Reproduction
In single-celled animals, cell division allows them to reproduce. The cell simply divides into
two identical, but smaller, cells when it is fully grown.
This type of reproduction only requires one parent and is called asexual reproduction.
All offspring produced by asexual reproduction are genetically identical to each other and
are called clones.
An example of an organism that reproduces asexually is yeast.
Yeast reproduce by a process called budding.
Binary fission is another type of cell division carried out by single celled organisms, such as
Amoeba which allows them to reproduce.
growth
young
cell mature
cell
cell division
Daughter cell
Daughter cell
Bud forming on the
single celled yeast
Parent
Amoeba Undergoing cell
division
2 daughter
Amoeba produced
Asexual Reproduction in Multicellular Organisms
Organisms such as plants can reproduce asexually. There are various structures produced by
plants to allow them to reproduce by this method such as runners (strawberry plants),
tubers (potato plants) and bulbs (daffodils).
Runners
Tubers Bulb
(Potato Plant) (Daffodil)
Advantages and disadvantages of sexual and asexual reproduction
Type of reproduction Advantages Disadvantages
Sexual Increases variation Requires to parents
Relies on fertilisation
Asexual Only requires 1 parent
Doesn’t rely on fertilisation
All organisms are genetically
the same
Fertilisation in animals
To increase the number of organisms in a population depends on the process of fertilisation.
Fertilisation is when the nucleus of the male sex cell fuses with the nucleus of the female
sex cell.
There are two methods of fertilisation – internal, mainly used by land animals, and external
used by aquatic animals. Internal fertilisation is where the sperm and egg join inside the
female. With external fertilisation the sperm and eggs are released into the surrounding
water where they join.
Examples of animals that use external
fertilisation are fish and amphibians.
Examples of animals that use internal
fertilisation are birds and mammals.
Egg cell
(Female sex cell)
Sperm cell
(Male sex cell)
Fertilisation
Fertilised Cell
Fertilisation in plants
Fertilisation occurs when the nucleus of both the male and female sex cells fuse together.
This occurs following the process of pollination (when the pollen is transferred from the
male part (anther) of one plant to the female part (stigma) of another). The male nucleus
travels down a pollen tube towards the ovary where the female sex cells are produced. Once
inside the ovary the male nucleus will fuse with the nucleus of the female sex cell.
Once the ovule has been fertilised the ovule becomes a seed and the ovary becomes a fruit.
This is the means by which a plant reproduces. The seeds are dispersed and when the
conditions are favourable they will grow into a new plant.
Pollen grain
Female sex cell
Ovary
Pollen Tube
Dandelions produce seeds
that are carried by the wind.
A new plant will grow
wherever the seed lands if
the conditions are favourable
Strawberry plants produce seeds on
the surface of the fruit. When
eaten by animals the seeds pass
through the digestive system and
are deposited in faeces. A new
plant will grow wherever the seed
lands if the conditions are
favourable.
Development
In mammals internal development occurs, which means that the
embryo develops inside the female’s reproductive system.
Compared with bird development this has a number of
advantages such as the developing embryos are kept warm, fed
and protected by one or both parents.
In birds their eggs have to be incubated because they need to
be kept warm for the embryos to develop. After the eggs
hatch, parental care of the young is essential because they cannot fly or feed themselves at
first.
In trout the fertilised eggs begin to develop and
when they hatch the trout fry feed on food from
their yolk sac. Once they are free-swimming and
the mouth has developed they feed on small
aquatic animals.
Increasing Chances of Survival
Animals which have external fertilisation, e.g. trout and frogs, produce a great many more
eggs than animals which fertilise internally, e.g. birds and mammals.
With internal fertilisation there is a greater chance of sperm reaching the eggs and
fertilisation taking place. There is also less chance of the gametes becoming diseased. With
external fertilisation many of the eggs will get eaten by predators or will not get fertilised
as the sperm and eggs drift away from each other. As there is a greater chance of survival
with internal fertilisation, it is possible to produce fewer eggs.
Land animals need to use internal fertilisation so that the sperm can swim to the egg or, as in
the case of amphibians, return to the water to breed.
As mammals also have internal development and look after their young after birth, this
means that they can produce even fewer eggs than other groups of animals.
yolk sac
The number of young surviving can be calculated using the following formula:
Number of = fertilised eggs – (diseased eggs + eggs eaten + young eaten)
young surviving
The percentage of the young surviving can be calculated using the following formula:
% = Total young surviving x 100
Total number of eggs produced
Examples of the survival chances of different species
Species Total no.
eggs
produced
No. of
eggs
fertilised
No. of
fertilised
eggs
diseased
No. of
fertilised
eggs
eaten
No. of
young
eaten
Total
young
surviving
% survival
Rabbit 8 8 0 0 4 4 50
Trout 3000 2000 200 800 850 150 5
Human 1 1 0 0 0 1 100
Pheasant 15 12 2 2 3 5 33
2.2. - Propagating and Growing Plants Summary
GGrroowwiinngg PPllaannttss ffrroomm SSeeeedd
TTyyppeess ooff SSeeeeddss
SSoowwiinngg SSeeeeddss
Level and gently firm the compost. Spread the seeds as evenly as possible on the surface of the compost. Cover the seeds with a thin layer of compost (unless the seeds need light). Water the seeds with a fine spray from a watering can. Write your name, date, type and variety of seed on a plant label and insert it into the
seed tray or pot. Cover the tray or pot with a clear plastic lid to maintain the humidity. Leave in a warm place to maintain a suitable temperature.
Type of seed Method of sowing Advantage
Large seeds (e.g. broad bean)
Individually
spread out
Reduces competition
for light, water,
space and minerals
Very small seeds
Mixed with sand Helps to sow the
seeds more evenly
Pelleted (enclosed
in a ball of clay)
Seeds are easier to
handle and can be
sown more evenly
Chitted seeds (pre-germinated)
Individually
spread out
Seed coat split to
allow germination
before sowing
This picture shows an electrically
heated propagator with three
seed trays with plastic lids.
A thermostat can be set to
maintain the correct temperature
for the germination of the seeds.
VVeeggeettaattiivvee PPrrooppaaggaattiioonn
VVeeggeettaattiivvee pprrooppaaggaattiioonn iiss aa ffoorrmm ooff aasseexxuuaall rreepprroodduuccttiioonn uusseedd bbyy ppllaannttss wwhhiicchh pprroodduucceess cclloonnee
ooffffsspprriinngg.. TThheerree aarree mmaannyy mmeetthhooddss ooff vveeggeettaattiivvee rreepprroodduuccttiioonn,, eexxaammpplleess ooff wwhhiicchh aarree
oouuttlliinneedd bbeellooww..
BBuullbbss aanndd TTuubbeerrss
Bulbs store food. They have buds which produce flowers or daughter bulbs. Since these are
produced from one parent, this is a method of vegetative propagation.
The food store allows bulbs to withstand winter conditions and to grow early in the spring
before seeds germinate.
Tubers are another example of a food storage organ e.g. potato
a daffodil bulb
AAttttaacchheedd OOffffsspprriinngg
Some plants produce miniature plants called plantlets attached to the parent.
The plantlets obtain food from the parent plant until they have produced roots and can
absorb water and minerals from the soil.
11.. PPrroodduuccttiioonn ooff PPllaannttlleettss ffrroomm RRuunnnneerrss
In the case of Spider Plant and Mother of Thousands, the plantlet forms at the end of a
runner (a horizontal stem).
The plantlet can be 'pegged down' into a small pot of compost using wire.
When roots are established, the runner is cut close to the new plant and the wire removed.
Strawberry plants can also be propagated by this method.
2. Production of Leaf Plantlets
The Mexican Hat Plant produces large
numbers of small plantlets along the
leaf edges. These can be detached from
the leaf and grown in pots of compost.
Spider Plant Mother of Thousands
cut after
rooting
runner
young plant
parent plant
runner
young
plant
parent plant
plantlets
plantlet
The Piggyback Plant produces plantlets in the
middle of its leaves.
3. Production of Plants from Offsets
Some plants, for example Mother-in-Law’s Tongue, produce
offsets. Offsets are small plantlets produced as side shoots at
the base of the parent plant.
These can be detached from the parent plant and grown
separately.
AArrttiiffiicciiaall PPrrooppaaggaattiioonn
AArrttiiffiicciiaall pprrooppaaggaattiioonn iiss aa mmeetthhoodd ooff pprrooppaaggaattiinngg ppllaannttss wwhhiicchh iiss ccaarrrriieedd oouutt bbyy hhuummaannss;; tthhiiss
ttyyppee ooff pprrooppaaggaattiioonn iiss nnoott aa nnaattuurraall mmeetthhoodd uusseedd bbyy ppllaannttss.. Artificial propagation means that
part of a plant, for example a stem or leaf, is cut off from its parent and treated so that it
grows into a new plant.
This method is quicker than waiting for the parent plant to produce seeds and all new plants
will be exactly like the parent plant e.g. same colour of flower and leaves.
MMeetthhooddss ooff aarrttiiffiicciiaall pprrooppaaggaattiioonn aarree ddeessccrriibbeedd bbeellooww..
1. Taking Stem Cuttings
Nodes are points on a plant's stem where new growth occurs. When a plant stem is wounded,
for example by cutting below a node, the stem produces roots. Rooting powder can also be
used which speeds up root growth.
Cuttings are placed in propagators, these have electrical cables that supply heat to the
cuttings to encourage root growth.
If too much heat is supplied, the plant will wilt as it loses too
much water. This can be prevented by reducing the leaf surface
area by removing some of the lower leaves or by increasing the
humidity by placing the cutting in a propagator or covering it with
a polythene bag.
Commercial plant growers use mist propagation to maintain a high
level of humidity in the air around the cuttings by continually
spraying a very fine mist of water into the air.
offset
Taking a Cutting
2. Layering
Layering is a method of propagating plants which have long flexible stems.
When the stem is still attached to the parent plant, it is 'pegged down' into a pot of rooting
compost or into the soil if it is an outdoor plant. Often the stem is wounded by cutting below
a 'node' (point where leaves are attached) and dusted with rooting powder to encourage root
growth.
When roots develop, the stem is cut to separate the new plant from the parent plant.
The advantage of 'layering' is that the new
plant is supplied with water, food and
minerals from the parent plant. This means
that many plants which are difficult to raise
from cuttings can be propagated by this
method. The plants produced are also
larger.
Step 1 A diagonal cut is made in the stem
just below a node (i.e. where leaf
joins the stem).
Step 2 Remove the lower leaves of the
cutting to reduce water loss.
Step 3 Dip the cut end of the stem into rooting
powder to encourage the growth of roots.
Step 4 Carefully place the cutting into a hole in the
centre of compost in a plant pot. Gently firm
the compost by pressing down around the cutting.
Step 5 Water the compost.
Step 6 Place the potted cutting in a propagator with a
lid to increase humidity and reduce water loss
from the cutting.
stem of parent
plant
new plant
PPrrootteecctteedd CCuullttiivvaattiioonn
Protected cultivation involves growing plants in a sheltered enclosure (e.g. a greenhouse) in
which the environment can be controlled.
11.. GGrreeeennhhoouusseess aanndd PPoollyytthheennee TTuunnnneellss
Greenhouses and polythene tunnels protect plants from cold, wind, rain and frost.
HHeeaattiinngg GGrreeeennhhoouusseess
To control the temperature in a greenhouse, the electricity supply is
connected to a thermostat. When the temperature falls below a fixed
temperature the thermostat switches the heating on and switches it off
when a fixed upper temperature is reached.
The advantage of heating is that it prevents frost damage and
encourages plant growth.
The disadvantage is that the plant may lose too much water and wilt.
Ventilation of Greenhouses
Ventilation means providing fresh air. Stale moist air provides ideal conditions for the spread
of disease for example grey mould (mildew).
Ventilation is also important in controlling temperature and humidity (how much moisture is in
the air).
To provide the best conditions for plant growth, automatic ventilation is essential. Automatic
systems work without anyone being there to operate them. The two main automatic systems
for controlling ventilation are automatic window openers and thermostatically controlled
electric fans.
polythene tunnel greenhouse
22.. FFllooaattiinngg FFlleeeeccee aanndd CClloocchheess
Floating fleece and cloches also protect plants from the weather.
Cloches are tent-like structures made from glass, plastic or
polythene.
Plastic or polythene cloches are the most common type
nowadays being cheaper and less likely to break than glass.
Floating fleece is a light material which allows the
plants to grow under it, protecting the plants from
frost while still allowing water and light to pass
through.
2.3. Commercial uses of plants
Plants are used for many different things and have become an enormous industry, on which
the entire world depends.
Some of the most common uses for plants are:
Food
Raw materials
Medicine
Fuels
Food
Agriculture or the production of plants for use as a food stuff, vital industry for all people in
the world. Of the land on planet earth, almost 40% is currently used for the production of
crops for food and there is the potential for even more land to be used in this way.
Some of the most important crops in the world are: Rice, Corn, Wheat and Potatoes.
Corn – A staple food for the majority of sun-Saharan
Africa, corn is both easily grown and is edible with
very little preparation.
Wheat – Covers more of the earth than any other crop
and grows well in almost all climates making it a better
general crop than rice or corn. Wheat is also the major
source of vegetable protein for humans
Rice – A staple crop for the majority of Asia and is more
important than corn as rice’s sole use is as a food (corn
has other used which will be discussed later). Rice
accounts for 1/5 of all the calories consumed by humans.
Raw Materials
The most obvious use of plants as raw materials is Timber
wood, used to make frames for buildings, buildings
themselves, boats and any number of smaller items made
from wood. Oils extracted from plants (sunflower oil) can
be used for things such as cooking. One of the most used
plants is the cotton plant, which is used to make clothes
for people all over the world.
Medicines
Another common commercial use for plants is in medicine. Some of the most well-known
medicines are mass produced in this way, for example: Willow trees are used to produce Aspirin for helping with pain
(among other things).
Opium poppies are used to produce morphine, a very strong
pain killer.
Quinine, made from the bark of Cinchona tree, is used to
treat malaria.
Fuels
A less well-known use of plants is in the production of fuels. Wood
can be used as a basic fuel, however more and more we are looking
for new ways to create sustainable energy for future generations.
Corn is mass produced to make ethanol, which when mixed with
gasoline, is used as gasohol. Sugar cane is also grown for this use, in
particular in South America and Australia.
Effect of population on plant production
The increasing population of the world has put greater demand on the production of plants in
particular the use of plants as food stuffs is incredibly important. As the population
increases, more forward planning and attention must be paid to the conservation and
management of plant species.
World population & growth rate World grain production
Pharming techniques
Pharming techniques involve the genetic modification of plants in order to improve the plant
yields or the development of new products.
This process involves the inserting of a gene into an existing plant species in order to create
an improved variety of that species. An example of this is the insertion of pesticide
resistance into oil seed rape plants, therefore less plants will be lost as waste.
The most used role of pharming is in the insertion of genes used to produce medicines;
this allows pharmaceuticals to be produced at a lower cost and in greater numbers. Some
examples of medicines currently being produced in this way are: hormones, antibodies and
vaccines.
There are however, disadvantages of producing plants in this way, some of which are:
The potential transfer of inserted genes (i.e. disease resistance) into wild
varieties of plant
The lack of information on how GM foods affect human health
Unexpected toxin could be produced by these plants
The development of GM crops is expensive
In short: The DNA for the
gene that is looking to be
expressed, is extracted and
inserted into the plant by using
enzymes.
Once the plant is fully grown,
the product is extracted and
sterilised then is used in the
form of a medicine