Bio Plants

What is Transpiration

Transpiration is the loss of water vapour from the leaves of a plant, caused by evaporation of water from the surfaces of mesophyll cells followed by diffusion of water vapour through the stomata into the air.

Whta are the factors affecting transpiration (4)

Air Movement

Humidity

Temperature

Light Intensity

How does high air movement affect the rate of transpiration

Increases the rate

Good air flow removes water vapour from the air surrounding the leaf which increases the conc gradient between the leaf and the air increasing water loss

How does high humidity affect the rate of transpiration

Decreases the rate

When the air is saturated with water vapour (high humidity) the conc gradient is less so less water is lost

How does high light intensity affect the rate of transpiration

Increases the rate

Guard cells are responsive to the light intensity

When it is high, they are turgid and the stomata open allowing water to be lost

How does high temperature affect the rate of transpiration

Increases the rate

Particles have more kinetic energy, so transpiration occurs at a faster rate. Water molecules evaporate from the mesophyll cells and diffuse out through the stomata faster than they do at lower temperatures.

Diagram of plant tissue and exchange of substances through the Stoma

What is the role of the waxy cuticle

Prevents water loss by evaporation

What is the role of the upper epidermis

Thin and transparent to allow light to enter the palisade mesophyll layer underneath it

What is the role of the palisade mesophyll?

Column shaped cells tightly packed with chloroplasts to absorb more light TO MAXIMISE PHOTOSYNTHESIS

What is the role of the spongy mesophyll

Contains internal air spaces that increase the SA:V ratio for the diffusion of gasses mainly CO2

What is the role of the lower epidermis

Contains guard cells and stomata

What is the role of the Guard cells

Guard cells open and close the stomata, controlling gas exchange and water loss.When guard cells take up water they become turgid and the stomata open, allowing CO2 to diffuse in for photosynthesis and O2 and water vapour to diffuse out. When guard cells lose water they become flaccid and the stomata close, reducing water loss.

What is the role of the Stomata

Where gas exchange takes place

Opens during the day,closes during the night

Evaporation takes place here

Found in much greater concentration on the underside of the leaf to reduce water loss

What is the role of the vascular bundle

Contains xylem and phloem to transport substances to and from the leaf

What is the role of the Xylem

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

What is the role of the Phloem

Transports sucrose and amino acids around the plant

How is the leaf best adapted for optimal diffusion and photosynthesis

Large SA, which increases the SA available for diffusion of CO2 and absorption of light for photosynthesis

Thin- allows Co2 to diffuse to palisade mesophyll cells quickly

How is the network of veins best adapted for optimal diffusion and photosynthesis

"The extensive network ensures xylem can supply water close to every cell (shortening diffusion distance for photosynthesis)

How is the Epidermis best adapted for optimal diffusion and photosynthesis

Its thin and transparent- allowing more light to reach the palisade cells

How is the cuticle best adapted for optimal diffusion and photosynthesis

It is thin and made of wax- to protect the leaf without blocking sunlight

How is the palisade layer at the top of the leaf best adapted for maximum light absorption

The palisade layer is situated near the upper surface with tall, tightly packed cells containing dense chloroplasts to maximize sunlight absorption for photosynthesis.

How is the spongy later best adapted for optimal diffusion

It has air spaces- whcih allow CO2 to diffuse through the leaf, increasing the SA

What is meristem tissue

Unspecialised actively dividing cells that are responsible for growth

Where is meristem tissue found

In the roots and shoots of plants

Describe the movement of water from the soil to the plant

From soil into root hair cells

Soil has a higher water potential than the root hair cells.

Water moves by osmosis through the partially permeable membrane into the root hair cells.

From root hair cells into xylem

Cells closer to the xylem have a lower water potential.

Water moves by osmosis from cell to cell until it enters the xylem vessels in the root.

Up the xylem to the leaves

Water moves up the xylem as a continuous column by transpiration pull (mass flow), helped by cohesion between water molecules.

From xylem in the leaf to outside air

Water moves by osmosis from xylem into mesophyll cells, then evaporates into the air spaces.

Water vapour then diffuses out through the stomata to the outside air.

What is a trophism

A growth response to a stimulus

What is phototrophism

A response to light

What is geotrophism

A response to gravity

Does Auxin diffuse to the shaded or bright side when light is directional on a plant?

Shaded side, causing those cells to elongate resulting in the shoot bending and growing towards the sunlight

What is Positive tropism

The plant grows towards the stimulus

What is negative tropism

Plant grows away from stimulus

What are shoots response to gravity and light

They grow up

Positive phototropic response

Negative geotropic response

What are roots response to gravity and light

They grow down into the soil

Negative phototrophic response

Positive geotropic response

What is the role of Auxins

Hormones that control cell elongation in plants

Where are auxins mostly made

In the tips of growing shoots

If light shines all around the tip not directionally what happens to the distribution of Auxin

Auxin is distributed evenly throughout and the cells in the shoot grow at the same rate

What is the role of IAA (auxins) in the shoots

Higher IAA concentration stimulates cell elongation which bends the plant toward the stimulus

What is the role of IAA (auxins) in the roots

Higher IAA concentration inhibits cell elongation causing the roots to bed downwards

What is the purpose of a clinostat in experiments

Is used to eliminate the effects of gravity, allowing observations of plant growth responses

What is a clinostat

An apparatus that rotates plants to study their growth responses

What is an isotonic solution

Same water potential as the cell.

No net movement of water in or out.

Cell keeps its normal shape (not swollen or shrunken).

What is a hypertonic solution

Lower water potential outside than inside the cell (more concentrated solution outside).

Water moves out of the cell by osmosis.

Cell shrinks and becomes wrinkled - this is a crenated cell.

What is a hypotonic solution?

Higher water potential outside than inside the cell (more dilute solution outside).

Water moves into the cell by osmosis.

Cell swells and may burst (lyse)

What is a plasmolysed cell

A plasmolysed cell is a plant cell that has lost so much water by osmosis (in a hypertonic solution) that the cell surface membrane pulls away from the cell wall.

What is a turgid cell

A turgid cell is a plant cell that has taken in water by osmosis (in a hypotonic solution) until the vacuole is full, the cytoplasm is pressed against the cell wall, and the cell becomes firm.

What is plasmolysis

the process where cells lose water in a hypertonic solution causing the cell membrane to pull away from the cell wall.

What is the Xylem's Function and Direction

Transports water and mineral ions from roots to stems and leaves

Unidirectional (upwards)

What is the Xylem's structure and support

Xylem vessels are composed of dead, hollow cells with no cytoplasm and no end walls, forming a continuous tube for the transport of water and mineral ions.

Lignin strengthens the cell walls

What is the Xylem's process and does it require energy

Part of the transpiration stream

Does NOT require energy

What is the function and direction of the Phloem

Transports sucrose and AA from leaves to the rest of the plant

Bidirectional (up&down)

What is the structure and support of the Phloem

Phloem consists of living sieve tube elements joined end to end, with sieve plates between them and very little cytoplasm, plus companion cells alongside that contain a nucleus and many mitochondria to provide energy.

Sieve plates between cells allow for substances to pass through

What is the process that the Phloem carry's out and does it require energy

Translocation (transport of sugars from sources to sinks (roots fruits ect))

Requires energy

What is the cell's state in the Xylem compared to the Phloem

Xylem=dead

Phloem=living

What are the specialised cells in the Phloem called

Sieve tubes

Companion cells

What are sieve tubes and what do they do

They are specialised cells for transport

NO nuclei

Each sieve tube has a perforated end so its cytoplasm connects one cell to the next

What are companion cells and what do they do

One or more companion cells attached to each sieve tube provides energy for transport of substances

A sieve tube is completely depended on its companion cell.

Gives sieve tubes energy and provides it with genetic material.

How are the root hair cells adapted for their function in the roots

They have a long, thin root hair extension, giving a large surface area for absorption of water and mineral ions.

They have a thin, partially permeable cell membrane and cell wall, giving a short diffusion pathway for water entering by osmosis.

They contain many mitochondria, providing energy (ATP) for active transport of mineral ions from the soil.

Passage of water into the mesophyll cells from the soil

Soil

Root hair cells

Cortex

Xylem vessels

Veins of leaf

Mesophyll cells