Plant growth

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How are plants adapted to growth?

Different parts of a plant are adapted to assist its growth and survival.

Flowers are adapted to enable reproduction.

Stems support the plant and transport nutrients.

Leaves are adapted for photosynthesis, which makes materials for growth.

Roots anchor the plant to the ground. They also take up water and minerals from the soil.


How tall can plants grow?

The tallest known plants are the Coast Redwoods, found in the USA. These grow to over 100 metres tall. That’s twice the height of Nelson’s column!

The tallest native European tree is the Caucasian Fir, which can reach a height of 68 metres.

Eucalyptus trees imported from Australia to Spain have been known to grow to a height of 80 metres.


How big can plants grow?

The Giant Sequoia, Sequoiadendron giganteum, does not grow as tall as the Coast Redwood but it has a larger volume.

The largest, General Sherman, has a volume of almost 1,500 m3, about half the volume of an Olympic swimming pool.


What is the oldest plant in the world?

Bristlecone pines, found in the USA, are the oldest-known plants. They can live for over 4,000 years.

Unlike animal cells, there is no limit to the number of times plant cells can divide and multiply.

It is common for trees to live for 100 years but rare for animals to live this long. Why?

Plant cells can differentiate to form specific cells throughout the plant’s life. Animal cells lose this ability early in their life cycle.


What do plants need to grow?

This plant hasn’t been looked after very well. What do plants need to grow healthily?

sunlight and an air supply

water

mineral nutrients.

If a plant cannot get these from its environment, can it move to somewhere else?

Plants are rooted to one place. However, they can control their direction of growth.


What controls plant growth?

Plants grow in response to their environment.

The shoots of these tulips grow upwards and the roots grow downwards.

To what environmental factors do plants respond to make sure they grow properly?

If a plant was unable to do this it might not be able to get enough water or sunlight from its environment.


What do plants respond to?

Plants are very sensitive and their growth is affected by their environmental conditions.

Any condition that affects plant growth is called a stimulus.

light water gravity

Which stimulus will have the strongest effect on the plant?

What are three types of stimuli that plants respond to?


Which stimulus?



A tropism is a growth movement in response to a stimulus.Plants grow towards or away from stimuli.

A growth movement towards a stimulus is called a positive tropism.

A growth movement away from a stimulus is called a negative tropism.

What is a tropism?

Will all the parts of a plant respond to a stimulus in the same way?

What is growth away from a stimulus called?


Plant responses to stimuli are given specific names:

What do the names of each tropism mean?

water gravitylight

hydrotropism geotropismphototropism

Which parts of a plant respond to these different stimuli?

Are there different types of tropisms?


Defining tropisms


How do tropisms affect growth?

This plant does not have a very straight stem. What might have caused this?

The shoots of plants grow towards sunlight.

The plant was placed on a window sill and received light from one direction only.

What is the name of this type of plant response?

The response to sunlight is called phototropism.


Phototropism experiment


Do plants have hormones too?

The growth of shoots and roots is controlled by a group of hormones called auxins. These chemicals are produced in the tips of the shoots and roots.

Like humans, plants use hormones, (chemical messengers)to control their development.

Hormones produced by plants control growth, flowering and fruit ripening.

What environmental stimuli might cause a plant to produce auxins?


Hormones and phototropism


Discovery of auxins


Which way up?

How do plants always grow the right way up?

Plants respond to gravity to grow in the right direction.


Hormones and geotropism


Roots always grow towards water, which is a positive tropism.

Roots will grow sideways, or even upwards, towards water.Roots always have a stronger response to water than gravity to ensure that a plant gets the water it needs.

How do roots respond to water?


How do roots and shoots respond to stimuli?

Shoots grow towards sunlight. They are positively phototropic.

Plant stimuli affect certain parts of the plant in different ways.

Shoots grow away from gravity. They are negatively geotropic.

Roots grow away from sunlight. They are negatively phototropic. Roots grow towards gravity. They are positively geotropic.

What experiments can be used to test these ideas?


Tropisms and auxins – true or false?



growing cuttings

killing weeds.

ripening fruit

Why are these purposes useful for gardeners and farmers?

Plant hormones are naturally-occurring chemicals but they can also be produced synthetically for use in gardening and agriculture such as:

How can plant hormones be used?


A cutting is a part of plant that is removed from the main shoot. Do cuttings have everything they need to grow?

How are cuttings grown?

A cutting does not have roots and so has no supply of water or minerals.

To stimulate root growth, cuttings are dipped into rooting powder. This contains plant growth hormones.

Cuttings are genetically identical to the parent plant. This allows growers to copy successful plants.


Growing plant cuttings


Weeds are unwelcome plants that compete with the plants being grown by gardeners and farmers.

How do plant hormones kill weeds?

Plant hormones can be used instead to make weedkillers that only affect certain plants.

However, many chemicals that are potential weedkillers are toxic to animals and humans, as well as plants.

Most weeds have broad leaves. Cereals, which have narrow leaves, can be protected from weeds by using weedkillers that only effect the growth of broadleaved plants.


Fruit often has to travels thousands of miles from where it is picked to where it is sold in the shops.

How are hormones used to ripen fruit?

When the fruit reaches its destination, it can then be sprayed with artificial plant hormones to encourage ripening.

Fruit is often picked before it is fully ripe. Why might this help keep the fruit edible?

Unripe fruit is harder and less likely to bruise than ripe fruit when transported.

Why might it be a good idea to wash fruit before eating it?


Which hormone makes fruit ripen?

Using artificial ethylene to ripen fruit is not just a modern practice. Ancient Egyptians exposed figs to natural gas, which contains ethylene, to encourage ripening.

Ethylene is a plant hormone that controls fruit ripening. It can be sprayed on unripe fruit to speed up ripening.

Why might it be important to keep fruit away from coal-burning engines during transportation?

Some fruit, such as bananas, actually produce a large amount of ethylene, which can cause other nearby fruits to ripen.



What do plants need for a balanced diet?

Plants need carbon dioxide and water for photosynthesis.Do they need any other nutrients to keep healthy?


What minerals do plants need?

Plants also need mineral ions for healthy growth.

Some of the most important minerals needed by plants are:

The mineral ions are found in salts, dissolved in water.Plants obtain minerals when they absorb water from the soil.

How do plants obtain these minerals?

nitrogen

potassium ions

phosphorus

potassium

magnesium magnesium ions

phosphates

nitrates

What type of salt are each of these elements found in?


Mineral ions are used by plants for growth and to build new cells.

making proteins for growth

respiration and making roots

respiration and photosynthesis

making chlorophyll

Mineral element How mineral is used in plants

nitrogen (N)

phosphorus (P)

potassium (K)

magnesium (Mg)

What are minerals used for?

Plants need a variety of minerals because they are used by the plant in different ways.

How are the four key mineral ions used by plants?


How do minerals affect cell formation?

nitrogen is needed to make amino acids and proteins

phosphorus is needed to make DNA and cell membranes

potassium helps enzymes work during photosynthesis

magnesium is needed to make chlorophyll.

Minerals form the building blocks of vital cell components:

What would happen to the plant if it was not able to get these nutrients?


Which mineral?


Plants do not grow properly and begin to look unhealthy if they are deprived of minerals.

If a plant does not get enough of a mineral it is said to have a mineral deficiency.

What happens when plants do not get minerals?

Do all mineral deficiencies affect a plant in the same way?


Mineral deficiencies and plant growth


Mineral deficiency


Where do minerals come from?

Rocks. The minerals in rocks are slowly dissolved by rainwater, which is slightly acidic. These minerals are washed into the soil.

What are the sources of minerals in the soil?

Why might farmers need to add fertilizers to their soil?

Natural fertilizers. Animal faeces and the decay of dead plants and animals return minerals to the soil.

Artificial fertilizers. These contain a ready-made mixture of the minerals needed by plants.


30% phosphorus

15% nitrogen

What are NPK values?

Fertilizers will often show NPK values on their labels. What do you think these letters stand for?

NPK stands for nitrogen (N), phosphorus (P), and potassium (K). Fertilizers contain these elements because plants need these nutrients in higher quantities than other minerals.

What percentage of each mineral is in a fertilizer with the NPK value 20–10–5?

The numbers show the percentage of each mineral element. This fertilizer contains:

15% potassium.


Artificial fertilizers



Glossary (1/2)

auxins – Plant hormones that control the rate of growth.

cutting – Part of a plant that has been removed from the main shoot and does not have roots.

ethylene – A plant hormone used to ripen fruit.

geotropism – A growth movement in response to gravity.

hydrotropism – A growth movement in response to water.

mineral deficiency – A condition that occurs when a plant is missing one or more of the minerals needed for growth.

mineral ions – Naturally-occurring or synthetic chemicals needed for healthy plant growth.


Glossary (2/2)

mineral salts – Compounds containing essential plant minerals.

negative tropism – A growth movement away from a stimulus.

NPK value – The percentage of nitrogen, phosphorus and potassium available in a fertilizer.

phototropism – A growth movement in response to light.

positive tropism – A growth movement towards a stimulus.

tropism – Any growth movement in response to a stimulus.


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Plant growth