Biology - Transport in Plants

What is a tissue ?

A group of similar cells carrying out the same function

What are the three plant tissues ?

Dermal, ground and vascular tissue

What is the dermal tissue ?

a single layer of cells that surrounds different parts of a plant

What is the function of the dermal tissue ?

To protect the plant

What is an example of dermal tissue ?

The epidermis

What is the function of the vascular tissue ?

To transport material around the plant

What are the two types of vascular tissue ?

Xylem and phloem

What is the ground tissue ?

Consists of cells located between the dermal and vascular tissues

What is the function of the ground tissue ?

To carry out many chemical reactions (such as photosynthesis and respiration) along with storing food and water

What are the two cells xylem are made up of ?

vessels and tracheids

What happen to the living contents of tracheids and vessels ?

They die before they reach maturity

What are xylem tracheids ?

Long, sloping or tapering cells whose insides are hollow at maturity

What are pits ?

What are xylem vessels ?

Tubular structures formed when a number of cells join end-to-end

What are vessels more efficient at than tracheids ?

Transporting water

What are vessels very common in ?

Flowering plants

What is lignin ?

a strengthening material found in some plant cell walls

What are cells that contain lignin said to be ?

Lignified

What do tracheids and vessels have ?

Thick, lignified cell walls (gives them great strength)

What is lignin laid down in ?

Definite patterns, the most common of which is spiral

What forms the wood in trees ?

Lignified xylem

What are the functions of xylem ?

Transports water and mineral salts from the roots to the leaves

Gives mechanical support to the plant (due to lignin)

Where is xylem found ?

Roots, stems, leaves, flowers and vascular bundles (special group of transporting cells)

What are the adaptations of xylem for the transport of water ?

They are narrow tubes

They are hollow (i.e. they have no cytoplasm)

They have no end walls (so they form a continuous tube)

They have pits (to allow horizontal movement of water)

They are strengthened with lignin (so they don’t collapse inwards)

What is mature xylem ?

a hollow dead tissue

What is phloem mainly composed of ?

Sieve tubes and companion cells

What are sieve tubes ?

Long, tubular structures

How do sieve tubes form ?

When individual cells, called sieve tube elements, join end to end

Why are the end walls called sieve plates ?

They resemble plates with numerous pores in them

What is the functions of the sieve tubes ?

Sieve tubes transport food made by photosynthesis from the leaves to the rest of the plant

Companion cells control the activities of the sieve tube elements

What does each sieve tube element have ?

An accompanying companion cell on its outside

What does each companion cell have ?

A nucleus and dense cytoplasm

Where is the phloem located ?

In vascular bundles in the roots, stems, leaves and flowers

What are the main things about xylem ?

Carries water and minerals

Is dead when mature

Has lignin

Has no companion cells

What are the main things about phloem ?

Carries food

Is living

Has no lignin

Has companion cells

What are flowering plants composed of ?

an underground root system and an above-ground shoot system

What does the zone of protection do ?

The root cap protects the root cells as they push through the soil

What is a meristem ?

A plant tissue capable of mitosis

What is the zone of cell protection also known as ?

The meristematic zone

What do the meristems allow the plant to do ?

To grow

Where are apical meristems found ?

In the root tip and shoot tip

Where are other meristems found ?

Around the edge of some plant stems and in leaves

What are cells in the root meristem doing ?

Constantly dividing by mitosis to produce new cells for growth

What happens when new cells are formed by the meristem ?

They are very small

What happens in the zone of elongation ?

Plant growth regulators (such as auxins) stimulate the cells to grow longer

What happens in the zone of differentiation ?

The elongated cells, which initially are all similar or undifferentiated, develop into different types of tissues (e.g. dermal, ground and vascular tissue)

What happens in the zone of differentiation ? (2)

As this is the zone that contains root hairs, the zone of differentiation is the zone in which water is absorbed

What are the functions of roots ?

Anchor the plant in the soil

Absorb water and mineral salts (the root hairs carry out this function)

Transport absorbed materials to the shoots

Store food in some plants (e.g carrots, turnips, radish)

What do herbaceous plants not contain ?

They do not contain wood (or lignin)

What do woody plants contain ?

Wood (or lignin)

What is the stem ?

The main part of the shoot

How is the stem in a herbaceous plant ?

Soft and green and does not contain wood

How is the stem in woody plants ?

Hard, woody and brown

What is a node ?

The point on a stem at which a leaf is attached

What is an internode ?

The region on a stem between two nodes

What is a bud ?

A potential growth point that may develop into a shoot, leaf or a flower

What does the tip of the stem have ?

A terminal or apical bud

What happens if the terminal or apical bud is removed ?

What is an axil ?

The angle between a leaf and a stem

What is a lenticel ?

An opening on a stem for gas exchange

What do scale scars represent ?

The locations of previous apical buds

What does the distance between two scale scars represent ?

One year of growth

What are the functions of stems ?

Support the aerial parts of the plant

Transport water and minerals from the root to the leaves and flowers

Transport food made in the leaves to the roots

Carry out photosynthesis (when they are green)

May store food (e.g. potato, bamboo and ginger)

What is a petiole ?

The stalk of a leaf

What is the lamina ?

A thin leaf blade

Why is the lamina a thin leaf blade ?

This is an adaptation to reduce the distances gases have to travel within leaves

What do the petiole, midrib and veins contain

Vascular or transport materials (xylem and phloem)

What are the functions of leaves ?

Make food (i.e. carry out photosynthesis)

Exchange gases with the atmosphere (in daylight they take in carbon dioxide and release oxygen and water vapour)

Lose water (in a process called transpiration): this allows fresh water and mineral salts to be taken into the plant and it may also cool the plant

Store food (this is why the leaves of plants such as grasses, lettuce and cabbages are often consumed by animals and plants)

What are the adaptations of leaves for photosynthesis ?

Most leaves have large leaf blades (to absorb as much light as possible)

They are thin (so that gases can easily pass form top to bottom and vice versa in leaves)

Stomata are openings on the bottom of the leaf (to allow gases to pass in and out, and by being on the underside of the leaf the stomata lose less water)

They have huge numbers of stomata (to allow maximum gas exchange)

What are the adaptations of leaves for photosynthesis ? (2)

Guard cells can open and close the stomata

Chloroplasts (and chlorophyll) are concentrated in the upper parts of the leaf (to absorb maximum light)

They have a large number of veins (to supply the leaves with water; to carry away the products of photosynthesis ; to support the leaf)

The cuticle is transparent and waxy (to allow light to pass through and prevent water loss)

What minerals do plants require to function normally ?

Calcium (for the formation of cell walls) and magnesium (for the formation of chlorophyll)

How are minerals absorbed into roots through root hairs ?

Some minerals are adsorbed by diffusion. This method does not require energy and is also called passive transport

Some minerals are adsorbed by active transport. This method uses energy in the form of ATP

What are the adaptations of the root hairs for absorption ?

Thin walls

Not covered by a cuticle

Very numerous, which provides a large surface area

How is water absorbed in the root hairs ?

Osmosis

How does osmosis work in root hairs ?

Soil particles are enclosed by a layer of relatively pure water

The cytoplasm of the root hairs contains many dissolved minerals

This means that the cytoplasm of the root hairs is more concentrated than the water in the soil

As a result, water enters the cytoplasm of the root hairs by osmosis

What is transpiration ?

The loss of water from a plant by evaporation

What is the transpiration stream ?

The flow of water from the roots to the leaves

What are the two sources of carbon dioxide for photosynthesis ?

From the atmosphere

Produced in leaf cells by the process of respiration

How is the true rate of photosynthesis calculated ?

Rate of carbon dioxide absorbed through the stomata + rate of carbon dioxide produced in respiration

What is the fate of oxygen ?

Oxygen produced in photosynthesis can diffuse into the air spaces of the leaf. Oxygen can then diffuse out through the stomata into the atmosphere

Oxygen formed in photosynthesis can be used in leaf cells for respiration

What is the fate of glucose ?

May be used immediately for respiration

May be converted to starch for storage

May be converted to another carbohydrate called sucrose

How do plants reduce their rate of transpiration ?

Leaves have a waxy cuticle. This is normally thicker on the upper surface of the leaf because more water can evaporate from the upper surface of a leaf than from the lower surface

Stomata are located on the lower surface of a leaf

Each stomata is surrounded by two guard cells

What mechanisms cause the movement of water from the roots to the upper parts of a plant ?

Root pressure and cohesion-tension

What does the cohesion-tension model explain ?

How water is transported in plants to great heights against the force of gravity

How does root pressure work ?

When water is drawn into roots by osmosis, the build-up of water causes a pressure. the root pressure pushes water up through the xylem

What is cohesion ?

The sticking of similar molecules to each other

What is adhesion ?

The sticking of different molecules together

Who created the cohesion-tension models ?

Henry Dixon and John Joly

How does cohesion tension model work ?

Water has a high cohesion. Water adheres to the walls of xylem, but this force is not as great as the cohesive forces of water

Water evaporates from the xylem to the air spaces of the leaf

As transpiration pulls each water molecule out of the xylem, the next water molecule is pulled with it, because of their high cohesion

This only works in narrow tubes such as xylem

When water molecules are pulled in this way, the entire column of water in the xylem is stretched. The water in the xylem is said to be under tension

Why do stems become slightly narrower in the day ?

Stomata open in daylight and transpiration occurs. The tension produced in the water column cause xylem to become narrower. This in turn causes stems to become slightly narrower by day

What happens when transpiration stops in the night ?

The lack of tension allows the xylem to return to its original shape

What are each stoma enclosed by ?

A pair of kidney shaped guard cells

What happens when there are high concentrations of carbon dioxide in the air spaces ?

The stomata close

What happens when there are low concentrations of carbon dioxide in the air spaces ?

The stomata open