The roles of plants in the environment
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The roles of plants in the environment. The Biosphere Depends on Plants. Cellulose: a large and complex carbohydrate We cannot digest it but can use it in different ways Examples: grass for cattle, Cottons, fabrics, paper, cardboard. 2. Plants as a Food Source.

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The roles of plants in the environment

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The roles of plants in the environment

The Biosphere Depends on Plants

  • Cellulose: a large and complex carbohydrate

  • We cannot digest it but can use it in different ways

  • Examples: grass for cattle, Cottons, fabrics, paper, cardboard


Plants as a Food Source

  • Agriculture: farming or forestry practices that produce food and goods

  • Humans use about 150 of the 50 000 edible plant species on Earth

  • Human diet is made up only about 20 crop plants

  • Wheat, rice and corn: 60% of calories come from plants

  • Other important crops: sugar cane, potatoes, sugar beets, soybeans and barley

Wheat: 28,611

Canola: 12, 642

Barley: 11, 781

Grain corn: 10, 592

Oats: 4,722

Top Crops in Canada

  • 1 in 7 jobs in Canada is in agriculture

  • 10% of Canada’s GDP

Production (thousands of tons)

One type of plant is grown in place of the natural ecosystem

What are some pros and cons of this approach?

increase crop yield, ease of caring

nutrient depletion in soil, vulnerable to pests, require synthetic fertilizers


Food Security

  • Sustainable Agriculture

  • An approach to agricultural production that integrates economics, the environment and society in meeting the nutritional needs of the world

  • Crop rotations, natural predators, laborers vs. machines


Medicinal Uses

25% of prescription medicines contain plant extracts

Rosy periwinkle (vincristine and vinblastine) – childhood leukemia and Hodgkin’s. Survival rates have gone from 20% to 90% with these 2 compounds

Ginseng – immune system function

Plants as a Source of Biochemicals


Coals –decomposed plants buried deep underground

Biofuels: fuels that are produced from renewable biological sources

Most biofuels come from corn (ethanol).

1 L of fossil fuel to produce 1.25L of corn ethanol

Corn prices


The paradox of farming: farmers need good soil to farm, yet farming destroys good soil.

About 1/3 of the country's topsoil has been lost due to urbanization and soil erosion.

Soil erosion can be reduced by covering the area with plants

Erosion Control

Movement mechanism of substances in plants

How many drops of water can you fit on a penny?

Water Movement

The theory is based on the 3 properties of water:

  • Cohesion: the ability of water molecules to stick together

  • Adhesion: the ability of water molecules to stick to the sides of hollow tubes.

  • The high surface tension of water.

Cohesive properties of water allows some bugs to “walk” on water

Plant cells in different types of solutions

  • firm and turgidnot very firmcells shrink

  • Plant cells prefer being turgid.



Plasmolysed after being placed in a concentrated solution of sucrose.


  • 90% of water that enters the leaf is lost out of stomata through transpiration

  • How is water transported 100m up without muscles?

  • Positive pressure (pushing)

    • Root pressure

  • Negative pressure (pulling)

    • Transpirational pull

Water Movement

  • Water is moved up from the roots, up the stem and out of leaves by the Transpiration-Pull Theory (Cohesion-Tension pull theory).

Osmosis: Solutes sucks

  • During osmosis, water will move from an area of low solute (e.g. salt, sugar) concentration to an area with high solute concentration.

Transpiration: Obtaining water

  • Leaves must obtain water from the soil. How does water get from roots to leaves?

  • 1) Active transport: Root hairs suck in a whole bunch of solutes.

  • 2) Osmosis: Water enters root hairs through osmosis.

  • 3) Root pressure: As water builds up in root, pressure rises enough to push water up a bit, but not enough to reach leaves.

  • 4) Transpiration: Water makes its way from the roots to the leaves by travelling through the xylem cells as it evaporates.

  • NOTE: Evaporation of water from the stomata of the leaf pulls the water up the roots and stem during transpiration.

Root hairs absorb ions and minerals. Water follows by osmosis.Water will make its way to the xylem cells.As pressure builds, water goes up the xylem.Root pressure is not enough to carry water up to the leaves.

1) Sun causes water to evaporate and exit the leaves through stomata.

2) As the water exits the leaves, it pulls on water molecules below dragging them up from the roots to the leaves.

3) Cohesion (attachment of water molecules to each other) allows for water molecules to come up together.

4) Adhesion (attachment of water to xylem walls) prevents water molecules from going back down to roots.


Transpiration- Simply putTeach this concept to your partner

  • 1) Water leaves the leaf as it evaporates through the stomata.

  • 2) Because of cohesion, the water molecules drag other water molecules up the roots, stem, and to the leaf.

  • 3) Adhesion stops the water molecules from falling back down (gravity).

Sugar Movement

  • This process is known as the Pressure-Flow Theory

  • Glucose is created at the leaf (The Source) during photosynthesis. Glucose is changed into the disaccharide sucrose in order to be transported in the plant.

Sugar Movement

  • This sucrose is actively transported (uses energy) into the phloem cells in the leaf.

  • There is a high concentration of sugar (sucrose) in the phloem at the source.

Sugar Movement

  • Because there is so much sugar in the phloem, some water moves in from the xylem to try and balance out the concentration (i.e. osmosis of water)

  • This creates a high amount of pressure in the phloem near the source.

Sugar Movement

  • Meanwhile sugar is being actively transported into the root or any other storage area in the plant (The Sink).

  • Sinks have lots of sugar (usually joined together to form starch).

  • The phloem cells around a sink have low amounts of sugar and therefore water will leave them and cause them to have a low amount of pressure.

  • Due to the difference in pressure in the phloem cells at the Source and the Sink, sugar will be forced down the phloem along this pressure gradient.

Sugar Movement

Plant Growth and Development

Plant Growth Regulators (PGRs)

  • Plants produce chemical compounds (hormones) that act as chemical signals between different parts of the plant

  • Hormones affect the rate of division, elongation and differentiation of plant cells

  • Five well-characterized groups of PGRs

  • Auxins

  • Gibberellins

  • Cytokinins

  • abscisic acid

  • ethylene

Produced in plants at the apical meristem (stems and roots)

Regulate cell expansion in plant responses to light and gravity

1. Auxins


1. Auxins

Auxins promote elongation of cells, stimulate growth and ripening of fruit, and also inhibit the dropping of fruit and leaves.

Synthetic auxins can be used to stimulate growth of fruit from unpollinated plants, resulting in, for example, seedless tomatoes.



2. Gibberellins

  • Also produced in the apical meristem

  • promote cell division and elongation taller and stronger plants

  • Sometimes they cause a process called bolting where the stem of a plant rapid grows taller before flowering.

  • Used in commercial crops to increase fruit size

Lettuce bolting after it has been treated with gibberellins.

3. Cytokinins

  • stimulate cell division, differentiation and leaf growth.

  • Delay the ageing of leaves and fruit

  • Commercially, cytokinins are used to extend the life of cut flowers.

4. Abscisic Acid

  • Abscisic acid’s main role is to coordinate responses to stress in plants.

  • Usually inhibits growth.

  • induces dormancy of seeds to protect them from harsh conditions and also regulates rate of transpiration.

Maple tree seeds. Some seeds can remain dormant for years and still be viable in newfound hospitable conditions.

5. Ethylene

Ethylene is a gas produced in many of the plant’s tissues.

  • It plays a role in flower death, fruit ripening and fruit loss.

  • Growers can delay ripening of fruit until they are about to be sold by controlling the levels of ethylene in the fruit.

External Factors that Regulate Plant Development


  • (hydronasty)

Plant’s tropic responses

  • Phototropism

  • Gravitropism

  • Thigmotropism

  • Stress??


  • Movement of plants as they growth towards LIGHT

  • For example, a plant growing in uneven light will lean and bend its stem in order to become better exposed to the light.


  • Growth or movement of a plant in response to gravity

  • If plants could not detect and respond to gravity, their roots would be as likely to grow up into the air as down into the ground.

the stem is trying to grow back upwards and fight gravity.


  • Growth or movement of a plant in response to touch

  • For example, the tendrils of pea plants will grow around a supporting structure at the point of contact.

Plant Reproduction: Alternation of generation

  • Both sexual and asexual reproduction occur.

  • All plants have a life cycle involving alternation of generations

  • Both a haploid gametophyte and a diploid sporophyte are stages in the reproductive cycle of plants.

Dissecting a flower activity

  • In group of 4

  • Dissect and identify all the structures of the flower

  • Draw a diagram and label all the structures of the flower that you’ve identified

Anatomy of a flower

Anatomy of a flower

Anatomy of a flower

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