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