Unit 8 - Transport in Plants

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Questions and Answers

What role does evaporation from the surfaces of spongy mesophyll cells play in transpiration?

It increases humidity around the stomata.

It cools the plant down by using heat to convert water into vapor. (correct)

It warms the plant to enhance photosynthesis.

It reduces water loss by closing the stomata.

As the temperature increases, what effect does it have on the rate of transpiration?

The rate of transpiration decreases significantly.

The rate of transpiration fluctuates unpredictably.

The rate of transpiration remains unchanged.

The rate of transpiration also increases. (correct)

What happens when the rate of transpiration from the leaves increases?

Evaporation ceases completely until it stabilizes.

Water molecules are pushed down into the roots.

Water is pulled up the xylem vessels more quickly. (correct)

Water is pulled up the xylem vessels more slowly.

Which component of the plant is primarily responsible for the movement of dissolved products from source to sink?

Phloem tubes. Signup and view all the answers

What is the primary factor that leads to wilting in plants?

More water evaporating than can be absorbed by the roots. Signup and view all the answers

How does wind speed affect the rate of transpiration?

Increased wind speed increases the rate of transpiration. Signup and view all the answers

What structural feature of phloem tubes aids in the transport of substances?

Sieve plates in end walls. Signup and view all the answers

During what time of the year would storage organs typically serve as a source for sucrose?

Spring, during active growth periods. Signup and view all the answers

What occurs when a plant experiences wilting?

Cells lose turgor pressure due to lack of water. Signup and view all the answers

What effect does humidity have on transpiration rates?

High humidity decreases transpiration rates. Signup and view all the answers

What is the primary role of phloem vessels in plants?

Carry food materials from leaves to non-photosynthesising parts Signup and view all the answers

Why do root hair cells significantly increase the rate of absorption?

They increase surface area for absorption Signup and view all the answers

What causes water movement through xylem to occur in one direction only?

Absence of cross walls in xylem vessels Signup and view all the answers

Which process is mainly responsible for the entry of water into root hair cells?

Osmosis Signup and view all the answers

What is one of the main functions of transpiration in plants?

To help cool the leaves of the plant Signup and view all the answers

Which of the following structures are responsible for the strengthening of xylem vessels?

Lignin Signup and view all the answers

What happens to the xylem cells as they mature and take on their functional role?

They die and lose their cytoplasm Signup and view all the answers

In which part of the plant does osmosis first cause water to enter?

Root hair cells Signup and view all the answers

What is the correct pathway taken by water in a plant?

Root hair cell → root cortex cells → xylem → leaf mesophyll cells Signup and view all the answers

Which material is primarily transported by xylem vessels?

Water and dissolved minerals Signup and view all the answers

Study Notes

Transport in Plants

Plants use xylem and phloem vessels for transport
Xylem transports water and minerals from roots to stems and leaves
Phloem transports food (e.g., sucrose, amino acids) from photosynthetic leaves to other parts of the plant (non-photosynthetic)
Xylem cells are connected end-to-end, forming a continuous tube
Xylem cells have no cross walls allowing for free flow of water
The outer walls of xylem vessels are thickened with lignin, providing support for the plant
Water moves through the plant by osmosis
Water is drawn from the roots to the leaves through the transpiration stream
Transpiration is the evaporation of water from leaves (through stomata)
The cohesion and tension theory describes the mechanism of water movement in the xylem, relying on cohesion between water molecules and tension created by transpiration.

Root Hair Cells

Root hairs increase the surface area for water and mineral absorption from soil.
Water enters root hair cells by osmosis (from higher to lower water potential)
The pathway for water is: root hair cell → root cortex cells → xylem cells → leaf mesophyll cells

Investigating Water Movement

Placing a plant in a beaker of dyed water allows observation of the water pathway
Dye will show the pathway of water in the xylem vessels.

Transpiration

Transpiration is the loss of water vapour from plant leaves
Transpiration is a major pathway for water movement in plants.
Transpiration happens through stomata (openings on leaves).
Stomatal opening and closing is influenced by light and water availability.

Xylem Structure

Xylem vessels are dead cells that form a continuous tube
Xylem walls are thickened with lignin, providing support
Xylem cells are arranged end-to-end

Transpiration Stream

Transpiration creates a pull (tension) on water molecules in the xylem
Cohesion between water molecules helps water move up the stem

Transpiration Factors

Temperature: Higher temperatures lead to increased transpiration rates
Wind speed: Higher wind speeds lead to increased transpiration rates
Humidity: Lower humidity leads to increased transpiration rates
Light: Increased light intensity generally increases transpiration rates due to increased stomatal openings.

Translocation

Translocation is movement of sugars and amino acids around the plant
Phloem transports sugars and amino acids from source (where it is produces during photosynthesis) to sinks (where it is stored/used)
Phloem tubes are living cells with perforated end walls (sieve plates)
Translocation is a bi-directional process, moving in different directions depending on the plant's needs and the time of year.

Wilting

If the rate of water loss through transpiration exceeds the rate of water uptake, plants wilt.
This is caused by the loss of turgor pressure in cells, affecting the support of the plant

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Description

This quiz covers the key mechanisms of transport in plants, focusing on xylem and phloem functions. Learn about how water and nutrients move through plants and the roles played by root hair cells. Test your understanding of transpiration, osmosis, and the cohesion and tension theory.