Plant Systems

What is the primary function of a plant's leaves?

Leaves are responsible for photosynthesis and gas exchange.

What is the main responsibility of a plant's roots?

Roots are responsible for the uptake of water and dissolved minerals from the soil.

What is the primary role of a plant's stem?

Stems contain vascular bundles (xylem and phloem) for transporting materials between leaves and roots.

Why are leaves typically broad, flat, and thin?

This shape maximises their surface area for light absorption and gas exchange.

The outer surface of a leaf is covered by a waxy _, which serves as a hydrophobic barrier to prevent water loss.

cuticle

What is the function of stomatal pores on the underside of a leaf?

They facilitate the exchange of respiratory gases and water vapour.

Which cells flank the stomatal pores and regulate gas exchange?

Guard cells.

What is the name of the tissue layer in the leaf's interior where photosynthesis occurs?

Mesophyll.

What is the upper layer of the mesophyll called, and what is its key feature?

The palisade mesophyll, which consists of tightly packed cells containing many chloroplasts for light absorption.

What is the lower layer of the mesophyll called, and how is it adapted for its function?

The spongy mesophyll, which consists of loosely packed cells with many air spaces for gas exchange.

In a leaf's vascular bundle, what substance does the xylem transport?

Xylem transports water and minerals from the roots.

In a leaf's vascular bundle, what substance does the phloem transport?

Phloem transports dissolved sugars produced by the leaves.

What is the function of root hairs on the outer epidermis of a root?

They are protrusions that maximise the surface area for absorption.

What is the primary function of the cortex, the middle layer of a plant root?

It primarily functions as a storage site for starch.

What is the role of the Casparian strip in a plant root?

It surrounds the vascular bundle and allows the movement of water to be tightly regulated.

In a dicotyledonous root, where are the xylem and phloem located within the vascular bundle?

The xylem is located centrally, while the phloem is located in outer clusters.

In the stem of a dicotyledonous plant, how are the vascular bundles arranged?

They are arranged into concentric bundles around the outer edge of the stem.

Within a stem's vascular bundle, the is located on the inner side and the is on the outer side.

xylem, phloem

What is the function of the cambium layer in a plant stem?

It separates the xylem and phloem and provides undifferentiated cells for lateral growth.

Term: Plan Diagram

Definition: A drawing of tissues showing their outlines and relative proportions, without including any cells.

In plan diagrams of leaves, where is the xylem located relative to the phloem?

The xylem is located on the upper facing side, while the phloem is on the lower side.

What is transpiration?

Transpiration is the loss of water vapour from the stems and leaves of a plant.

How does transpiration create a hydrostatic pressure gradient?

Water evaporation from leaves and water uptake by roots creates a gradient that draws water up the xylem.

What happens to water in the spongy mesophyll when light is absorbed by a leaf?

The light energy converts the water into vapour through evaporation.

How does the evaporation of water from the spongy mesophyll lead to more water being drawn from the xylem?

It lowers hydrostatic pressure, creating a negative pressure potential (tension) that pulls water from the xylem via capillary action.

How do roots absorb water from the soil?

They absorb water via osmosis, driven by a high solute concentration within the root cells.

How do root cells create a hypertonic environment to draw in water?

They actively transport mineral ions into the root, increasing the solute concentration.

What do root cells actively expel to displace mineral ions from negatively charged clay particles?

H+ ions (protons).

What property of water molecules allows them to associate with each other, aiding in mass flow?

Cohesion.

What property of water molecules allows them to associate with the xylem wall, aiding in mass flow?

Adhesion.

The combination of cohesion and adhesion allows water to move in a continuous, _ column within the xylem.

unidirectional

What is a key structural adaptation of xylem vessels regarding their cellular composition?

They are lined by a layer of dead cells fused together to form a continuous hollow tube.

How is the cell wall of a xylem vessel adapted for mechanical strength?

It contains thickened cellulose and is reinforced by lignin.

What are the two types of cells that compose xylems?

Tracheids (all vascular plants) and vessel elements (only certain vascular plants).

How is water loss from the leaves regulated?

It is regulated by the opening and closing of stomata.

What hormone is released by dehydrated mesophyll cells when a plant starts to wilt?

Abscisic acid (ABA).

What does abscisic acid (ABA) trigger in guard cells?

It triggers the efflux of potassium from the guard cells.

How does the efflux of potassium from guard cells cause the stomatal pore to close?

It decreases water pressure (turgor) in the cells, making them flaccid and causing them to block the opening.

Why is transpiration described as an inevitable consequence of gas exchange in a leaf?

The stomata must be open for gas exchange for photosynthesis, which also allows water vapour to escape.

How does high temperature affect the rate of transpiration?

High temperatures increase the vaporisation of water, leading to a greater rate of diffusion and thus higher transpiration.

How does sunlight affect the rate of transpiration?

Sunlight stimulates the opening of stomata to allow for gas exchange during photosynthesis, thereby increasing transpiration.

How does wind affect the rate of transpiration?

Wind removes the layer of water vapour surrounding the leaf, increasing the concentration gradient and thus the rate of diffusion.

How does high humidity affect the rate of transpiration?

A higher concentration of water vapour in the air decreases the diffusion gradient from the leaves, lowering the transpiration rate.

What term describes the transport of water up the stem against gravity due to a hydrostatic pressure difference?

Mass flow.

What process occurs in the roots to facilitate water uptake?

Osmosis.

What process occurs in the leaves that initiates the transpiration pull?

Evaporation.

The transport of mineral ions from the soil into root cells, facilitated by the active expulsion of H+ ions, is a form of ____-.

indirect active transport

Which specialised proteins may be present in root cells to optimise water uptake?

Aquaporins.

What is the approximate percentage of water absorbed by roots that is lost through transpiration?

Over 95%.

How do tracheids differ from vessel elements in the xylem?

Tracheids are tapered cells that exchange water via pores, while vessel elements are fused cells allowing for faster transfer.