B4- Plant Biology

The leaf is…

A plant organ

What does the waxy cuticle do?

Protective layer on the top of the leaf that prevents water from evaporating

What does the upper epidermis do?

Thin and transparent to allow light to enter the palisade mesophyll layer easily

What does the spongy mesophyll do?

Contains air spaces that increases the surface area to volume ratio for the diffusion of gases

What does the lower epidermis contain?

Guard cells and stomata

What do the guard cells do?

Absorbs and loses water to open and close the stomata to allow carbon dioxide to diffuse in and oxygen to diffuse out.

What does the stomata do?

It is where gas exchange takes place. Opens during the day and closes during the night. Evaporation occurs here as well. In most plant, higher concentration of stomata is found on the bottom side to reduce water loss.

What does the vascular bundle do?

Contains the xylem and phloem to transportsubstances to and from the leaf

What does the xylem do?

Transport water into the leaf for the mesophyll cells to use in photosynthesis and for transpiration in the stomata

What does the phloem do?

Transportssucrose and amino acids around the plant

What is the adaptation of large surface area in leaves?

Increases surface area for the diffusion of carbon dioxide and absorption of light for photosynthesis

What is the adaptation of being thin in leaves?

Allows carbon dioxide to diffuse into the palisade mesophyll cells more quickly

What is the adaptation of chlorophyll in leaves?

Absorbs light energy so that photosynthesis can take place

What is the adaptation of network of veins in leaves?

Allows transport of water from cells of the leaf and carbohydrates from the leaf for photosynthesis

What is the adaptation of stomata in leaves?

Allows carbon dioxide to diffuse into the cell and oxygen to diffuse out

What is the adaptation of epidermis being thin and transparent in leaves?

Allows more light to reach the palisade cells

What is the adaptation of a thin article made of wax in leaves?

To protect the leaf without blocking sunlight

What is the adaptation of a spongy layer in leaves?

Air spaces allow carbon dioxide to diffuse through the leaf, increasing the surface area

What is the adaptation of a palisade cell layer at the top of the leaf in leaves?

Maximises the absorption of light as it will hit the chloroplasts in the cells directly

What is the adaptation of vascular bundles in leaves?

Thick cell walls of tissue in the bundles to help support the stem and leaves

What process happens in the xylem?

What is the xylem’s direction of flow?

Transpiration stream

One way from roots to leaves (unidirectional)

What process happens in the phloem?

What is the phloem’s direction of flow?

Translocation

All directions (bidirectional)

What cells are in the xylem and how does it’s adaptation help?

Dead cells to help in efficient transport of water absorbed by roots to other parts of the plant. Resistance to water flow is low

What cells are in the phloem and how does it’s adaptation help?

Living cells are in the phloem and they transport substances in the phloem (which require energy)

What features do xylem cells have?

• Lignin- strengthen cell wall and waterproof elongated cells

• No end walls- successive cells make a long tube for easy transport

• Dead- means the tube is hollow, so resistance to water flow is low

What do root hair cells do?

Absorb water from the soil via osmosis. Mineral ions are taken up via active transport.

What features do root hair cells have?

• Long projections- they stick out from the cells and into the soil to increase surface area over which water and mineral ions can be absorbed

• Mitochondria- ensure there is enough energy for active transport of minerals up the stem

What happens if there is abundant water in the stomata?

When there is abundant water, the plant can afford to lose some, so it opens the stomata to allow gases for photosynthesis to move freely in and out of the leaf.

What happens when there is scarce water in the stomata?

The stomata closes in order to prevent further water loss, which is achieved by guard cells returning to a limp state.

What happens to the stomata during the time of day?

At night, the stomata closes because in the absence of sunlight, carbon dioxide is not required for photosynthesis. The only objective is to prevent water loss.

What factors increase the rate of transpiration?

Increase temperature, decreased humidity, increased light intensity, increased air flow

Why doesn’t increased humidity increase the rate of transpiration?

Increased humidity increases the amount of water in the air, making it harder for water to evaporate.

What do the holes in the end wall of the phloem allow?

Allow cell sap (which stores sugars, salts and amino acids) to pass through the cells

Photosynthesis is a ____ reaction.

Endothermic

What is the role of leaves?

Help plants to photosynthesise and absorb light

How are leaves adapted for photosynthesis?

• Broad- large surface area for light absorption

• Thin- short diffusion distances for gases

• Vascular bundles- to transport reactants and products

Word equation for photosynthesis

Carbon dioxide + water —> glucose + oxygen

Symbol equation for photosynthesis

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

What are the uses of glucose in photosynthesis?

• Used in the process of respiration

• Converted into insoluble starch for storage

• Used to produce fat or oil for storage

• Used to produce cellulose to strength the cell walls

• Used to produce amino acids for protein synthesis

What are the factors affecting the rate of photosynthesis?

Temperature, light intensity, carbon dioxide concentration, amount of chlorophyll

Photosynthesis is controlled by ______.

Enzymes

The higher the light intensity, ________. (factors affecting rate of photosynthesis)

The more light can be absorbed by the chlorophyll in the chloroplasts.

Chlorophyll absorbs light to transfer ___________. (factors affecting the rate of photosynthesis)

The energy required for photosynthesis.

The more chlorophyll that is present, _____________. (factors affecting the rate of photosynthesis)

The more light is absorbed

Dependant variable

The variable that is measured for each change

Independent variable

The variable that is changed

Control variable

The variable that stays the same

What is the transpiration stream?

The movement of water from the roots to the leaves

What are the three stage of transpiration?

1. Diffusion out of the spongy mesophyll cells

2. Evaporation of water from the surface of these cells into the air spaces

3. Diffusion out of the stomata into the atmosphere

What are the factors affecting the rate of transpiration?

Light intensity, temperature, wind speed, humidity