The World of Plants

Growing Plants

G Davidson

Structure of a seed• In order to reproduce,

flowering plants produce seeds.

• Seeds contain nearly everything required to start the growth of a new plant.

• A seed is made up of the embryo, a food supply (endosperm), both enclosed in a tough seed coat (testa).

TestaEmbryo

Plumule

Radicle

Germination

• Seeds can survive for many years in the ground.

• They appear to be dead.

• When conditions are suitable they burst into life and start the growth of a new plant.

• This is called germination.

GerminationWhat is needed for germination to be successful?

Germination

Oxygen??

Light??

Water??

Soil??

Heat??

How do we find out?? Investigate!!

Investigation• When setting up an

investigation we need to change something and this is called a ‘variable’

• We start by setting up the basic apparatus

• In this case it will look like this: Cotton wool

Seeds

Boiling tube

Investigation• Our variables will be:• Water• Light• Heat• Oxygen• So we now want our investigation to be 5 boiling tubes• 1. No light• 2. No water• 3. No heat• 4. No oxygen• 5. Everything (the “control”)

Germination

• So, just what do seeds need for germination?

• Water

• Oxygen

• Minimum temperature

Structure of a Flower

• Sexual reproduction occurs in plants as well as animals.

• The FLOWER contains the reproductive organs of a plant.

• Flowers of different plants may not be exactly alike, but they are built to the same basic plan.

Structure of a Flower

Structure of a Flower

Structure of a flower• Pollen is made inside

the anthers.• When they ripen the

pollen is released.• Pollen grains are like

specks of dust.• They contain the

MALE sex cell.• This has to reach the

egg cell (ovule) in the ovary.

Pollination

• Pollination is the “transfer” Pollination is the “transfer” of pollen from the anthers of pollen from the anthers of one plant to the stigma of of one plant to the stigma of another.another.

Pollination

• Most flowers rely on either the wind or insects to transfer their pollen

• It is often easy to tell the method of pollination used by a flower by its appearance.

• Insect pollinated flowers use animals such as bees, butterflies, birds & bats.

• Wind pollinated flowers have structures which make use of the wind.

Methods of PollinationInsect pollination Wind pollination

Have a scent No scent

Sticky, spiky pollen Large amounts of light pollen

Sticky stigma inside flower

Feathery stigmas hang outside the flower

Stamens surrounded by petals

Large stamens hang outside flower

Produce nectar Don’t produce nectar

Petals large & bright Petals small & dull

Insect pollination

e.g. e.g. Passion Passion flowerflower

Wind Pollination

e.g. Sedgee.g. Sedge

Fertilisation• Once the pollen has

landed on the stigma the male sex cell inside has to get to the female sex cell.

• To do this it has to grow a pollen tube down through the style.

• The stigma produces a sugary fluid to feed the growing pollen tube.

Fruit Formation• After fertilisation the fertilised ovule becomes

the seed• The ovary develops into the fruit• The fruits can help in seed dispersal depending

on what kind of fruit they are.• There are 2 kinds:

1. Dry fruits – e.g. poppy, lupin, dandelion, sycamore, etc…

2. Flesh fruits – e.g. tomatoes, plums, gooseberries, etc…

Seed Dispersal

• Once fertilisation has taken place, the flower withers and a seed and fruit are formed from the ovary.

• The seeds must be scattered as far away from the parent plant as possible.

• This avoids the new plants competing with the parent for vital resources.

• This “seed dispersal” is achieved in a variety of ways.

Animal (external)

• Seeds can be dispersed by animals.

• The seed has hooks which catch onto animals’ fur and are transported by the animal until they fall off and hopefully germinate elsewhere.

• E.g. Burdock

Animal (internal)

• Seeds can also be eaten by animals along with the fruit.

• The seeds pass through the animal and are deposited in the droppings elsewhere

• E.g. bramble

Wind Dispersal

• Plants can also use the wind to scatter their seeds and they use different mechanisms to achieve this.

• E.g. the poppy uses the “pepper pot” method

Wind Dispersal

• Ragwort, dandelions, cotton, etc. use the “parachute” method.

• Each seed has a number of small feather-like structures to help it float in the wind.

Wind Dispersal

• Some seeds have wings to help them fly in the wind.

• E.g. sycamore, ash, etc..

Explosive

• Some plants such as peas and gorse use pods which “explode” to fire the seeds away from the parent.

• As a pod dries, tensions are set up in the wall of the pod eventually causing it to split along two lines of weakness.

Plant Life Cycle

SEED

GERMINATION

STEMS & ROOTS

FLOWERS

POLLINATION

Plant Life Cycles

• All stages involved in plant reproduction take place continually year after year.

• Some plants can reproduce WITHOUT forming seeds.

• This is another form of reproduction• It only involves one parent • No sex cells are involved• It is called ASEXUALASEXUAL reproduction

Plant Life Cycles

• During asexual reproduction the parent plant produces new cells which eventually separate and become new independent plants.

• E.g. strawberry, spider plant, etc..

Plant Life Cycles

The “Mexican Hat” Plant produces plantlets around the edge of the leaves. These eventually fall off and develop into new independent plants.

Asexual Reproduction

• Asexual reproduction is quite common in plants

• It produces new plants with the same characteristics as the parent.

• There is no variation

• If the plant is resistant to a particular disease, then so will the offspring.

Asexual Reproduction• Plants produced in this way are often found

growing in clumps to reduce competition from other plants.

• Growth occurs very quickly because of available food store.

• It is successful as it does not involve the vulnerable stages of germination and early seedling growth.

• Plants which are all identical, formed in this way are called a CLONECLONE

Sexual & Asexual Reproduction

Asexual Sexual

Advantages Early quick growth

Reduced competition

Variety

Seeds dispersed

Disadvantages Overcrowding

Quality doesn’t improve &

weaknesses passed on

Gametes required

Limited food store in seeds

There are some important differences between these 2 methods of reproduction. Each method

has advantages and disadvantages.

Artificial Propagation

• Gardeners make use of a plant’s ability to reproduce asexually by using a method known as artificial propagation.

• Instead of growing seeds they take a small section of stem, root or leaf and under the right conditions these will grow into a full plant.

Taking Cuttings

Take a piece 100-150 mm long by snipping (a tip cutting - "a") or by tearing off a side shoot (a heel cutting - "b").

Remove all flowers and buds and all leaves to about half way up the stem.

Taking Cuttings

Make holes with a pencil or knitting needle in damp, potting mix in a small, clean pot. A suitable mix is a mixture of 75% washed river sand and 25% sieved peat moss (or, preferably, an environmentally-friendly peat alternative such as "Coco Peat").

Slice a small sliver of bark off the bottom 5 mm of tip cuttings ("a") or carefully trim the end of heel cuttings ("b").

Taking CuttingsDip the prepared end of the cutting into a root -promoting hormone powder, blow off the excess, place in the hole in the damp sand to about half its length and press the sand firmly around the cutting. Root-promoting hormones should be kept in a refrigerator when not being used and are also available as liquids or gels.

Place the pot of cuttings into a plastic ice-cream container (or similar) with a little damp sand or peat-moss in the bottom, cover with a plastic bag and seal with an elastic band or sticky tape.

Grafting

Grafting

Layering