5) Nutrition in plants

Why is there an interconnecting system of air spaces in the spongy mesophyll?

Allows rapid diffusion of carbon dioxide and oxygen into and out of mesophyll cells

Word equation for photosynthesis

Carbon dioxide + water -> glucose + oxygen With sunlight and chlorophyll

Describe the role of chlorophyll in photosynthesis

Chlorophyll is a green pigment that traps and converts light energy into chemical energy. The chemical energy is used to make organic carbohydrates like glucose from inorganic carbon dioxide and water.

Suggest how conditions in a glasshouse can be controlled to Ensure the maximum growth of plants

Conditions in a glasshouse such as light intensity, temperature, amount of carbon dioxide, amount of water, concentration of mineral salts in soil and soil pH can be optimised to Ensure the maximum growth of the plants. A computerised system can be used to monitor the conditions frequently so that the factors that affect the rate of photosynthesis of the plants are kept at optimum levels. In particular, the plants have to be kept at an optimal temperature because enzymes are involved in photosynthesis and are highly sensitive to temperature changes. More carbon dioxide can also be supplied to the plants to increase the rate of photosynthesis of the plants.

In which process are water molecules broken about and converted into their chemicals?

During photosynthesis, carbohydrates (sugars) are formed in the chloroplasts. In this process, water is broken down and converted into oxygen and hydrogen atoms in the presence of light.

Explain why the rate of photosynthesis is faster on a warm day than on a cold day.

Enzymes are needed to carry out photosynthesis and they are very sensitive to temperature changes. On a cold day, most enzymes are inactive, thus the rate of photosynthesis is low. As the temperature increases, the rate of and photosynthesis increases. The enzymes and substrates have more kinetic energy, thus more enzyme-substrate complexes are formed and more products are formed. On a warm day, the rate of photosynthesis is faster than on a cold because the enzymes are more active and catalyse reactions at a higher rate.

How do carbon dioxide and water enter the leaf?

In daylight when photosynthesise occurs, the carbon dioxide in the leaf is rapidly used up. The carbon dioxide concentration in the leaf becomes lower than that in the atmospheric air, so a diffusion gradient exists. Therefore, carbon dioxide diffuses from the surrounding air through the stomata into the air spaces in the leaf. The surfaces of mesophyll cells are always covered by a thin film of water so that carbon dioxide can dissolve in it. The dissolved carbon dioxide then diffuses into the cells.

How do guard cells control the size of stomata? (In sunlight)

In sunlight, the guard cells photosynthesise, concerting light energy to chemical energy. The chemical energy is used to pump potassium ions (K+) into the guard cells from neighbouring epidermal cells. Water potential of the guard cells is lowered. Water from neighbouring epidermal cells then enters guard cells by osmosis. This increases the turgidity of the guard cells and causes them to become swollen. The guard cells have a thicker cell wall on one side of the cell (the side around the stomata pore). This causes the swollen guard cells to become more curved and pull the atoms open

Describe how light energy is converted to chemical energy and stored in carbohydrates in plants (Light-independent stage part 2)

In the light-independent stage, enzymes use the hydrogen atoms and chemical energy from the light-dependent stage to convert carbon dioxide into glucose. Overall, light energy from the Sun is trapped by chlorophyll and stored as chemical energy in carbohydrates.

External features of a lead

Lamina or Leaf blade and petiole or leaf stalk

Why is there more chloroplasts in upper palisade tissue?

More light energy can be absorbed near the leaf surface

What is the function of the stomata present in the epidermal layers?

Open in the presence of light, allowing carbon dioxide to diffuse in and oxygen to diffuse out of the leaf

In the section through a leaf of a green plant, during exposure to bright light, which region contains most starch?

Palisade mesophyll cell contains the most number of chloroplasts, thus it photosynthesises most actively and it contains the most starch.

Which cells contain chloroplasts in a transverse section of a leaf?

Palisade mesophyll cell, spongy mesophyll cell and guard cell contain chloroplasts. Thus, they are able to carry out photosynthesis.

What is photosynthesis?

Photosynthesis is a multi-step process in which light energy is trapped by chlorophyll and converted into chemical energy. This chemical energy is then used to manufacture carbohydrates from inorganic carbon dioxide and water. Oxygen is released as a by-product during this process

What does photosynthesis require?

Photosynthesis requires carbon dioxide, light, chlorophyll, water and a suitable temperature

How can leaves be destarched?

Placing them in darkness for two days

How can we test for photosynthesis?

Presence of starch in leaves shows that excess sugars have been produced by photosynthesis

What gives an indication of the rate of photosynthesis?

Rate of oxygen production

Function of stomata

Stomata allow the exchange of gases like carbon dioxide and oxygen between the plant and its surrounding. Each stoma is enclosed by two guard cells which control its size. Thus, the stomata regulate the rate of diffusion of these gases and water vapour through them. On a sunny day, carbon dioxide enters the leaf while oxygen leaves the leaf through the stomata. At night, oxygen enters the leaf while carbon dioxide leaves the leaf through the stomata. During transpiration, water vapour leaves the leaf through the stomata

Limiting factors of photosynthesis

Temperature Light intensity Carbon dioxide concentration

How does the cuticle on upper and lower epidermis adapted to allow the plant to photosynthesise?

The cuticle is waxy and transparent. The waxy and transparent cuticle on upper and lower epidermis reduces water loss through evaporation from the leaf Transparent for light to enter the leaf

Structure and function of lamina ( How is lamina adapted for function )

The lamina has a large flat surface compared to its volume. This enables it to obtain the maximum amount of sunlight for photosynthesis. A thin and broad lamina provides a short diffusion distance for gases and enables light to reach mesophyll cells

Structure and function of Petiole

The petiole holds the lamina away from the stem so that the lamina can obtain sufficient sunlight and air. In some leaves, for example grasses and maize, the petiole is absent. Such leaves have Long laminae.

How do guard cells control size of stomata? (at night)

The potassium ions they have accumulated in the guard cells during the day diffuse out of the guard cells. Water potential in the guard cells is increased, causing water to leave the cells by osmosis. The guard cells become flaccid and the stoma closes

Describe how light energy is converted to chemical energy and stored in carbohydrates in plants (Light dependent stage part 1)

The process of photosynthesis occurs in two stages . They are the light-dependent stage and light-independent stage. In the light dependent stage, light energy is trapped by chlorophyll and converted into chemical energy. Water molecules are spilt into oxygen and hydrogen atoms. The oxygen produced is released as a by-product.

Describe the process photosynthesis (6m)

The process of photosynthesis occurs in two stages. They are light-dependent stage and light-independent stage. In light-dependent stage, light energy is trapped by chlorophyll and converted into chemical energy. Water molecules are split into oxygen and hydrogen atoms. The oxygen produced is released as a by-product. In light-independent stage, enzymes use the from the hydrogen atoms and chemical energy light stage to convert carbon dioxide into glucose. Overall, photosynthesis is a process whereby light from the Sun is trapped by chlorophyll energy and used to convert inorganic carbon dioxide and water into organic carbohydrate (glucose) and oxygen. Light energy from the Sun is converted into Chemical energy and stored in carbohydrates.

Suggest why light is a major factor affecting the growth rate of the trees

The trees can only carry out photosynthesis in the presence of light. Photosynthesis is a process whereby light energy is trapped by chlorophyll and used to convert inorganic carbon dioxide and water into organic carbohydrates (glucose) and oxygen. The glucose serves as a source of food and energy for the trees. The amount of light affects the amount of glucose produced, which in turn affects the growth rate of the trees

Two test-tubes, P and Q were set up each containing a solution of red hydrogen carbonate indicator. An aquatic plant was placed into tubes P and Q. Tube P was uncovered, tube Q was covered with black lightproof cover. The tubes were left in a warm room in sunlight for four hours. What would be the colour of the hydrogen carbonate indicator in the two tubes after four hours?

Tube P would be purple whereas Tube Q would be yellow

Which cells do not contain chloroplasts in the leaf?

Upper and lower epidermal cell do not chloroplasts

Where in their leaf will there be no conversion of light energy to chemical energy?

Upper epidermis. It does not contain chloroplasts, thus it cannot carry out photosynthesis and there will be no conversion of light energy to chemical energy.

How do you tell when a plant grows in the shade

When a plant reaches its maximum rate of photosynthesis relatively quickly at Low light intensity, and further increase in light intensity has no effect of the rate of photosynthesis

Where is the cords-section of a leaf converts energy to chemical energy?

Wherever contains chloroplasts as they contain the green pigment, chlorophyll which converts light energy to chemical energy

What is chlorophyll?

green pigment that absorbs light for photosynthesis

What is photosynthesis used for

• Provides food and energy to humans and other organisms • Produces oxygen and removes carbon dioxide form the air

What is stored food used for

• Sugar and digested fats are used mainly for energy production • Some sugars are used for building up cell walls • Amino acids are assimilated to form new protoplasm

What are the glucose in leaves used for?

• Used in tissue respiration to provide energy for cellular activities, or for formation of cell walls • Converted into sucrose, amino acids, proteins and fats • Excess is stored temporarily as starch in leaves