Nutrition and transport in plants Bio unit 1 sec 3 2026

Characteristics of palisade mesophyll (3)

1. Consists of elongated, closely packed, long and cylindrical cells

2. Contains many chloroplast(~80% of photosynthesis)

3. Cytoplasmic streaming allow efficient distribution of sunlight among chloroplasts

Characteristics of spongy mesophyll(4)

1. Consists of cells with irregular shape that are covered with a thin film of moisture

2. Numerous large intercellular air spaces among loosely packed cells

3. Fewer chloroplasts than palisade mesophyll

4. Contains vascular bundle

Characteristics of upper epidermis(2)

1. Single layer of closely packed cells

2. Covered by a waxy, transparent cuticle to allow light to pass through and prevent water loss

Function of guard cells and how guard cells carry out their function.

Guard cells regulates rate of transpiration by controlling the opening of stoma. Guard cells contain chlorophyll unlike other epidermal cells. When there’s high light intensity, chloroplasts in guard cells carry out photosynthesis, producing glucose, reducing its water potential. Water enters guard cells via osmosis, causing it to be turgid and opening the stoma. (Opposite is true in lower light intensity)

Characteristics of the cell wall of guard cells

Has a less elastic thicker inner cell wall/ more elastic, thinner outer cell wall

Function of stomata

Facilitates gaseous exchange of carbon dioxide, oxygen and water vapour between leaf and surroundings.

Function of vascular tissues

Performs long distance transport of materials between root and shoot systems

Function of xylem and how its adapted for its function (

Xylem transports water and dissolved mineral salts upwards from roots to other parts of the plant by being made up of dead cells with no protoplasm which are joined end to end without cross walls to form a long hollow tube to reduce resistance to water. It also provides mechanical support for the plant through lignified cell wall to prevent collapse of the xylem vessel due to trans[ipartio pull.

Function of phloem and how is it adapted to its function

Phloem transports manufactured food substances such as glucose and amino acids bi-directionally to other parts of the plant. it is made up of living sieve tube cells joined by sieve plates that have many tiny holes to allow the flow of sucrose and amino acids. Each sieve tube cell has a companion cell which contain many mitochondria to provide nutrients and energy for the sieve tube cells for metabolic processes and carry out active transport for translocation.

Location of phloem and xylem in the vascular bundle, relative to the upper surface of the leaf and to the Center of the stem

The phloem is located nearer the bottom of the leaf and outer edge of the stem. The xylem is located nearer the upper side of the leaf and inner edge of the stem.

Characteristics of the xylem and phloem in the root

Xylem is a star shape at the Center of the root. Phloem is found between the arms of the star shape

Function of roots and how its adapted

Root absorbs water by osmosis and mineral salts by active transport and diffusion.

1. Root has many mitochondria to release energy for active transport

2. Root has a large central vacuole to store sugars, amino acids and mineral salts to decrease w.p. of cell sap for higher rate of osmosis.

3. Root has a selectively permeable membrane to prevent leakage of mineral ions, maintaining low water potential.

4. Root has an elongated shape for higher surface area to volume ratio to increase rate of water uptake.

Function of the cambium

Cambium cells actively divide and differentiate into new xylem and phloem tissues to thicken the stem.

Describe the light DEPENDENT stage of photosynthesis

1. Light energy is absorbed by chlorophyll and converted to chemical energy.

2. Light energy is used to split water molecules into hydrogen atoms and oxygen via phtolysis

Describe the light INDEPENDENT stage

Hydrogen is used to reduce carbon dioxide to form 6-carbon sugars, using the chemical energy from the light dependent stage.

Function of glucose in plants(3)

1. Used for cellular respiration

2. Used to synthesise cellulose in the cell wall, amino acids and lipids

3. Excess glucose is stored as starch in leaves of converted to sucrose to be transported to other parts of the plant or stored in storage organs

What affects photosynthesis?

1. Temp

2. CO2 concentration

3. Light intensity

How is the leaf’s physical structures adapted to its function

1. They are flat and thin to increase surface area for faster absorption of sunlight

2. They are arranged opposite each other/alternating to not block each other

Define transpiration

Transpiration is the loss of water vapour through the aerial parts of the plants, mainly through the stomata of the leaves, as a result of respiration and photosynthesis in plants

Why is transpiration important?

1. Cools the plant through evaporation of water from the surface of the cells in the leaves.

2. Transports DISSOLVED mineral salts from roots to other parts of the plant through transpiration pull

3. transports water to the leaves for photosynthesis and other various plant parts to maintain cell turgor, allowing non-woody plant parts to maintain shape and upright position by turgor pressure

Fully describe transpiration pull

When water vapour diffuses out of the stomata, water vapour from the thin film of moisture on mesophyll cells replace the water loss then water vapour from mesophyll cells move into the thin film of moisture by osmosis, causing water potential of cell sap to decrease so water deeper inside the leaf moves to replace the water, resulting in a suction force on the water column in the xylem vessel.

What affects rate of transpiration?

As humidity increases, rate of transpiration decreases.

As air movement, temperature, light intensity increases rate of transpiration increases.

How do external factors affect rate of transpiration? (4) long answer btw

1. Water vapour that diffuses out of the stomata tend to accumulate outside the stomata. Wind blows away this layer of water vapour, causing a steep water vapour concentration gradient between the inside of the leaf and outside of the leaf , hence rate of transpiration increases as wind speed increases.

2. Intercellular air spaces are usually saturated with water vapour. When humidity is high, there is a softer WATEE VAPOUR CONCENTRATION GRADIENT between intercellular air spaces in leaf and surrounding air, thus rate of transpiration is lower. Hence, rate of transpiration decreases as humidity increases

3. As temperature increases, water molecules gain KE and move faster, thus rate of evaporation of water from mesophyll cells and rate of diffusion of water vapour out through the stomata increases. Hence rate of transpiration increases as temperature increases. HOWEVER, on extremely hot days, excessive water loss from guard cells may cause them to become flaccid resulting in stomata closure, causing rate of transpiration to decrease.

4. In the day, guard cells photosynthesise and become turgid. Stomata open and become wider, rate of transpiration increases as light intensity increases.

Describe translocation

Translocation is the transport of manufactured food substances in the phloem.

How is transpiration rate measured? Give 2 methods and the formula)What are the assumptions

Using a buble potometer and measuring the distance the bubble moves in a fixed period of time and using formula rate = change in volume/cm³ / time taken OR using a mass potometer and using the formula rate = loss in mass in g/time .Assume that rate of water uptake through roots is equal to rate of water lost through transpiration and the use of water in photosynthesis is negligible.

When does wilting occur

the turgor pressure in the lead mesophyll cells help to support the leaf and keep it firm. The cells lose their turgor when the rate of water loss through transpiration is higher than rate of water uptake by plant roots, hence, cells turn flaccid and the plant wilts, drooping the plant leaves and stems to reduce their surface area in contact with the sun’s heat rays, reducing water loss by transpiration to help the plant conserve water.