Biology B5

?

Photosynthesis

Equation for photosynthesis:

Carbon Dioxide + Water Oxygen+Glucose

Photosynthesis is an endothermic reaction. This means light is taken in from the surroundings. This is converted into glucose which provides energy for the plant.

Equation for respiration:

Glucose+ Oxygen Water+ Carbon Dioxide

  • Glucose molecules link together to make starch.
  • Starch is then brokendown to simpler substances
  • Moved into cytoplasm and used to make sucrose
  • Sucrose transported around plant and used for:
    • Starch
    • Glucose for respiration
1 of 19

Leaf Cell Diagram

2 of 19

Active Transport in Plants

(http://plantcellbiology.masters.grkraj.org/html/Plant_Cellular_Physiology4-Absorption_Of_Mineral_Nutrients_files/image017.gif)

3 of 19

The Root Hair Cell

How are root hair cells adapted to their function?

  • The root hair cell has a long finger like part that adapts to ensure there is a greater surface area.
  • The cell wall is very thing to shorten the distance of diffusion or osmosis.
  • There are many mitochondrion to provide energy to the plant. This energy is used in active transport.

(http://4.bp.blogspot.com/-BmYFqWRncC8/UYYHM9mrZPI/AAAAAAAANYk/_ZLE7jTSvQc/s1600/root+hair+cell+structure.png)

4 of 19

Transport in Plants (water)

(http://cliparts.co/cliparts/Acb/KAa/AcbKAa4oi.png)

The evaporation of water from leaves keeps them cool and helps move water up the plant. The flow of water into a root, up the stem and out of the leaves is called transpiration.

5 of 19

Xylem Vessels

Xylem vessels form tiny continuous pipes, leading from a plant's roots up into its leaves. Inside the vessels is an unbroken chain of water, dues to the weak forces of attraction between water molecules. Water is pulled up the xylem vessels in the stem as water evaporates from the xylem vessels in the leaves. As the water diffuses out of a leaf, more water evaporates from inside the xylem inside the leaf.

Xylem cells are dead!

6 of 19

Phloem

Plants make sucrose from the glucose and starch made by photosynthesis. Sucrose is translocated in the sieve tubes of the phloem tissue. The large central channel in each sieve cell is connected to its neighbours by holes, through which sucrose solution flows.

(http://www.biologyjunction.com/images/phloem.jpg)

7 of 19

Plant Adaptations

  • Leaves often have large surface areas to ensure they collect enough light.
  • The energy transferred by light is trapped by chlorophyll packed into discs inside the choloroplast.
  • This energy is then transferred to glucose during photosynthesis.
  • The chloroplasts in a cell can move towards light or away from it (as protection from damage by very bright light).
  • Carbon dioxide for photosynthesis diffuses into the leaf through stomata.
  • Leaves are hin so that carbon dioxide doe not have fair to diffuse.
  • Spongy mesophyll cells create air spaces, allowing gases to diffuse easily.
  • A network of xylem vessels supplies the water for photosynthesis.
  • Epidermis cells form the outer layers of a leaf, holding the leaf together and protecting the cells inside.
  • Epidermis cells are transparent, allowing light to pass through them easily.
  • They also produce a waterproof waxy cuticle, which helps prevent water loss.
  • The cuticle also helps water to stop micro-organisms and water entering the leaf.
8 of 19

Plant Hormones

What do hormones control in plants?

  • Anything relating to growth!
    • Roots and growth, seed germination, leaf fall, disease resistance, fruit formation+ ripening,  flowering time, bud formation.

Plants respond to stimuli to:

  • Avoid stress
  • Avoid being eaten
  • Enhance survival
  • Improve chances of having offspring
  • The way a plant grows is controlled by the hormones
  • These are sensitive to the environment and can make adjustments to help plants survive.
9 of 19

Gibberellin

  • Gibberellin stimulates seed germination, stem growth and flowering
  • Gibberellin promotes cell division and elongation of the stem
  • If a dwarf variety of plant is sprayed with gibberellin it will grow to the same height as a tall variety.

10 of 19

Cytokinins

  • Like gibberellin, promotes cell division. High levels of this hormone are found in the actively growing parts of the plant.
  • Plants mainly grow at the tips of the shoots, the leaves and the tips of the roots.
  • They are developing fruits and seeds.

(http://cdn.phys.org/newman/gfx/news/hires/2014/planthormone.jpg)

11 of 19

Ethylene

  • Ethylene ripens fruits
  • Fruit can be picked in an unripened form
  • This can make it easier to transport causing it less damage or bruising in transport.
  • When it arrives at it's destination it can be sprayed with ethylene.
  • This is how soft fruits from abroad are in our supermarkets and ripe.

(http://plantcellbiology.masters.grkraj.org/html/Plant_Growth_And_Development7-Plant_Hormones-Ethylene_files/image009.jpg)

12 of 19

Abscisic Acid

  • As the environment changes around a plant, other hormones become active.
  • Sometimes plants need to slow down their growth. This is the job of the hormone abscisic acid.
  • This hormone slows down the plants metabolism, so that it doesn't grow during winter.
  • If conditions become stressful slowing down or stopping growth can help a plant to survive.

(http://3.bp.blogspot.com/-tlT0Gmbne7A/UER7ohKadyI/AAAAAAAAA4s/EwrpaFdjwJM/s1600/aba.jpg)

13 of 19

Tropisms

14 of 19

Negative and Postitive Tropisms

  • When a plant shoot grows towards the light thay are called positively phototropic.
  • Root growth away from light could be considered as negative phototropism, although in reality it is gravity that dictates their growth direction.
  • When plant roots grow towardsgravity they are called positively geotropic. Shoot growth away from gravity would be called negative geotropism.

Tropisms are how plants respond to their environment

  • When sunlight is the stimulus this is known as phototropism.
  • Positive phototropism is where the plant grows towards the light. This happens at the shoot tip.
  • Negative phototropism is where the plant grows away from the light. This happens at the root.
  • When gravity is the stimulus this is known as geotropism.
  • Positive geotropism is where the plant grows in the direction of gravity. This happens at the roots.
  • Negative geotropism is where the plant grows opposing gravity. This happens at the root tips.
15 of 19

Auxins

Plant stems always grow towards the light. This growth is caused and controlled by auxin. If a plant recieves light from one side it will grow towards it. The auxin is produced at the tip of a new shoot. It makes cells elongate more on the shaded side of the shoot so it bends towards the light.

Hormome Auxin Auxin promotes growth!

When light shines from an angle:

  • Sunlight breaks down auxin
  • So the side of the tip that has most direct sunlight will have the least amount of auxin
  • Area of the plant that is more shaded will have more auxin
  • More growth on shaded side
16 of 19

Uses of Plant Hormones- Weed Killers

  • Artificial auxins makes some plants grow uncontrollably which can kill them.
  • Selective weed killers contain artificial auxins to kill plants with broad leaves.
  • Farmers can therefore kill weeds in a wheat field without affecting the crop.

17 of 19

Uses of Plant Hormones- Rooting Powders

  • Powder contains auxins
  • Cuttings are dipped in powder
  • Promotes root growth

(http://4.bp.blogspot.com/-_NE3VHP8OOs/UqYDblmf7xI/AAAAAAAABMg/1NENsHXMrss/s1600/rooting+powder.jpg)

18 of 19

Photoperiodism

Photoperiodism is the reeponse of an organism to the number of daylight hourse ina day. Some plants use this to flower at a certain time. Flower growers can override photoperiodism by spraying the plants with gibberellins.

Many plants only produce seeds after being pollinated, which then allows egg cells to form. Gibberellins can cause some plants to produce fruit without this, so giving us seedless fruits. Gibberellins can also be sprayed on some plants to make them produce bigger fruits.

19 of 19

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Photosynthesis and transpiration resources »