Transport In Plants

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Notes

Xylem & Phloem

**Xylem vessels** transport water and mineral ions from roots to leaves.
**Phloem vessels** transport sucrose and amino acids from sources to sinks.
Xylem and phloem are arranged in **vascular bundles** throughout the plant.
In cross-section, **xylem is on the inside** and **phloem on the outside**.
Xylem adaptations: cells joined end-to-end with no cross walls, dead and hollow, walls thickened with **lignin**.
Phloem consists of living cells with **sieve plates** at end walls for easy flow.

Root Hair Cells

Root hairs are single-celled extensions of root epidermis cells.
They grow between soil particles to absorb water and minerals.
Water enters root hair cells by **osmosis** (soil water has higher water potential).
Large surface area of root hairs increases rate of water uptake by osmosis and mineral ion uptake by **active transport**.

Pathway of Water

Water moves: root hair cell → root cortex cells → **xylem** → leaf mesophyll cells.
Water crosses the root cortex by osmosis.
Water is transported up the xylem to the leaves.
Pathway can be shown using a **stain/dye** (e.g., celery in dyed water); dye appears in xylem on cross-section.

Transpiration

**Transpiration** is the loss of water vapour from leaves by evaporation from mesophyll cells and diffusion through **stomata**.
Functions: transports mineral ions, keeps cells turgid, provides water for photosynthesis, cools leaves.
Water moves up xylem in a **transpiration stream** – continuous column pulled by cohesion.
Transpiration creates a **tension/pull** on water in xylem due to cohesive forces between water molecules.

Factors Affecting Transpiration Rate

**High temperature** increases transpiration rate (more evaporation).
**High wind speed** increases transpiration rate (removes water vapour, steepens diffusion gradient).
**High humidity** decreases transpiration rate (reduces diffusion gradient).
**Light intensity** increases transpiration rate (stomata open wider).
**Wilting** occurs when water loss exceeds water uptake; cells lose turgor and plant collapses.

Investigating Transpiration (Potometer)

A **potometer** measures transpiration rate by movement of an air bubble in a capillary tube.
Method: cut shoot underwater, set up airtight, dry leaves, introduce air bubble, record distance moved over time.
Factors investigated: temperature (warm/cold room), wind speed (fan), humidity (plastic bag), light intensity.
Further bubble movement in same time = faster transpiration.

Translocation

**Translocation** is the transport of sucrose and amino acids in phloem from source to sink.
Phloem is made of living cells with **sieve plates**; transport is **bi-directional** depending on plant needs.
Sources: photosynthesising leaves (summer) or storage organs (winter).
Sinks: growing regions (roots, shoots, fruits) or storage organs.

Cross-section of a leaf showing mesophyll cells, air spaces, stomata and vascular bundles.

Pathway of water from root hair cells through xylem to leaf mesophyll and out through stomata.

Practice questions

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1.Which of the following is the main function of xylem vessels in a plant?
Easy
- ATransport of water and mineral ions from roots to leaves
- BTransport of sucrose and amino acids from leaves to roots
- CTransport of carbon dioxide from leaves to roots
- DTransport of oxygen from roots to leaves
2.The diagram shows a root hair cell. Which process is primarily responsible for the entry of water into the root hair cell?
Easy
- AActive transport
- BDiffusion
- COsmosis
- DTranspiration
3.A student places a celery stalk in a beaker of red dye. After a few hours, a cross-section of the stem is cut. Which part of the stem will be stained red?
Medium
- APhloem
- BXylem
- CCortex
- DEpidermis
4.Which of the following correctly describes the process of transpiration?
Medium
- ALoss of water vapour from leaves by evaporation and diffusion through stomata
- BLoss of water droplets from leaves by guttation
- CUptake of water by roots from the soil
- DMovement of water through xylem from roots to leaves
5.Which environmental condition would most reduce the rate of transpiration?
Hard
- AHigh temperature and low humidity
- BHigh temperature and high humidity
- CLow temperature and low humidity
- DLow temperature and high humidity
6.Which of the following substances is transported in the phloem?
Medium
- AWater and mineral ions
- BSucrose and amino acids
- COxygen and carbon dioxide
- DStarch and cellulose
7.The diagram shows a cross-section of a leaf. Which labelled structure is the site of evaporation that contributes to transpiration?
Hard
- ACuticle
- BSpongy mesophyll
- CStoma
- DXylem
8.In a potometer experiment, which of the following would increase the speed of the air bubble?
Medium
- ADecreasing the temperature
- BIncreasing the humidity around the leaves
- CIncreasing the wind speed around the leaves
- DCovering the leaves with petroleum jelly

More questions

9.Which adaptation of xylem vessels allows for the continuous flow of water?
Hard
- ACells are living with cytoplasm
- BCells have cross walls to regulate flow
- CCells are dead and hollow, with no end walls
- DCells are lined with cuticle to prevent leakage
10.What is the main role of root hairs in water absorption?
Easy
- AThey secrete water into the soil
- BThey increase the surface area for absorption
- CThey actively pump water into the root
- DThey prevent water loss from the root
11.Which of the following is a correct sequence in the pathway of water through a plant?
Medium
- ARoot hair cell → xylem → root cortex → leaf mesophyll
- BRoot hair cell → root cortex → xylem → leaf mesophyll
- CRoot cortex → root hair cell → xylem → leaf mesophyll
- DRoot hair cell → root cortex → phloem → leaf mesophyll
12.During winter, a deciduous tree has no leaves. Which part of the plant acts as the source for sucrose and amino acids?
Hard
- ALeaves
- BStorage organs (e.g., roots)
- CStems
- DFlowers
13.The table shows data from four plants growing under the same conditions. Which plant will have the lowest rate of transpiration?
Hard
- APlant A: 36 leaves, average leaf area 53 cm², stomatal density 276 per mm², stoma diameter 19 μm
- BPlant B: 21 leaves, average leaf area 51 cm², stomatal density 247 per mm², stoma diameter 18 μm
- CPlant C: 24 leaves, average leaf area 45 cm², stomatal density 249 per mm², stoma diameter 15 μm
- DPlant D: 17 leaves, average leaf area 40 cm², stomatal density 151 per mm², stoma diameter 16 μm
14.A student uses a potometer to measure transpiration rate. After 10 minutes, the air bubble moves 8 mm. The experiment is repeated with a fan blowing towards the leaves. In 10 minutes the bubble moves 14 mm. What is the percentage increase in transpiration rate?
Medium
- A75%
- B57%
- C43%
- D175%
15.A plant shoot is placed in a solution of dye. Under which conditions will the dye move most slowly up the stem?
Medium
- Ahigh temperature, high humidity
- Bhigh temperature, low humidity
- Clow temperature, high humidity
- Dlow temperature, low humidity
16.Which graph correctly shows the relationship between transpiration rate and atmospheric humidity?
Hard
- AA straight line sloping downward from high transpiration at low humidity to low transpiration at high humidity.
- BA straight line sloping upward from low transpiration at low humidity to high transpiration at high humidity.
- CA horizontal line showing constant transpiration rate regardless of humidity.
- DA curve that increases then decreases.
17.A researcher measures the rate of water uptake by a plant shoot using a potometer. The shoot has a total leaf surface area of 200 cm². Water uptake is 4 cm³ in 2 hours. What is the rate of water uptake per hour per cm² of leaf surface?
Medium
- A0.01 cm³/h/cm²
- B0.02 cm³/h/cm²
- C0.1 cm³/h/cm²
- D0.04 cm³/h/cm²
18.In an experiment, two shoots of the same plant are placed in identical conditions except shoot A has all its leaves removed and shoot B retains its leaves. After three days, the spring balance readings (in grams) are most likely:
Hard
- Ashoot A 40, shoot B 40
- Bshoot A 40, shoot B 34
- Cshoot A 34, shoot B 40
- Dshoot A 34, shoot B 34
19.Which process is responsible for the movement of water from the roots to the leaves in a plant?
Easy
- ATranslocation
- BTranspiration pull
- COsmosis
- DActive transport
20.A potometer experiment is set up to investigate the effect of temperature on transpiration. Which step is essential for a fair test?
Medium
- AUsing different plant shoots for each temperature.
- BKeeping the wind speed constant.
- CWetting the leaves before each measurement.
- DPlacing the potometer in direct sunlight.
21.Which row correctly describes the direction of transport in xylem and phloem?
Hard
- AXylem: bi-directional; Phloem: unidirectional (up)
- BXylem: unidirectional (up); Phloem: bi-directional
- CXylem: unidirectional (down); Phloem: bi-directional
- DXylem: bi-directional; Phloem: bi-directional
22.A student investigates the effect of light intensity on transpiration using a potometer. The results are shown. At which light intensity (lux) is the transpiration rate highest?
Medium
- A1000 lux, bubble moves 12 mm in 10 min
- B2000 lux, bubble moves 18 mm in 10 min
- C3000 lux, bubble moves 24 mm in 10 min
- D4000 lux, bubble moves 30 mm in 10 min
23.What is the main function of root hair cells?
Easy
- ATo anchor the plant in the soil.
- BTo absorb water and mineral ions from the soil.
- CTo transport sugars to the leaves.
- DTo carry out photosynthesis.
24.The diagram shows a cross-section of a root. Which labelled structure is responsible for transporting water to the stem?
Hard
- AEpidermis
- BCortex
- CXylem
- DPhloem
25.A student sets up a potometer with a leafy shoot. After drying the leaves, the capillary tube is placed in water and an air bubble is introduced. Which step is essential to ensure that the movement of the bubble is due to transpiration only?
Medium
- ASealing all joints with Vaseline to make the apparatus airtight
- BCutting the shoot underwater before placing it in the potometer
- CAllowing the plant to adapt for 5 minutes before starting measurements
- DRecording the temperature and humidity of the room
26.In an experiment, a shoot is placed in a potometer and the air bubble moves 12 mm in 10 minutes. The shoot is then placed in a dark cupboard for 10 minutes, and the bubble moves 4 mm. Which conclusion is correct?
Hard
- ALight intensity increases transpiration rate because stomata open in light.
- BDarkness increases transpiration rate because stomata open wider at night.
- CLight has no effect on transpiration; the difference is due to temperature change.
- DThe experiment is invalid because the shoot should have been left in the light for 20 minutes.
27.The diagram shows a cross-section of a stem from a dicotyledonous plant. Which labelled region is the phloem?
Medium
- AA (outer ring of cells just inside the epidermis)
- BB (ring of cells with thick walls, towards the centre)
- CC (central pith region)
- DD (single layer of cells surrounding the stem)
28.A plant is placed in a beaker of water containing a red dye. After 4 hours, a cross-section of the stem is cut and examined under a microscope. Which part of the stem is most likely to be stained red?
Hard
- AThe xylem vessels
- BThe phloem sieve tubes
- CThe cortex cells
- DThe epidermis
29.Which of the following is the correct definition of transpiration?
Easy
- AThe loss of water vapour from plant leaves by evaporation and diffusion through stomata
- BThe movement of water through the xylem from roots to leaves
- CThe uptake of water by root hair cells from the soil
- DThe transport of sucrose in the phloem
30.A potometer is used to measure transpiration rate under different conditions. Which combination of conditions would cause the air bubble to move the fastest?
Medium
- AHigh temperature, low humidity, high wind speed
- BLow temperature, high humidity, low wind speed
- CHigh temperature, high humidity, low wind speed
- DLow temperature, low humidity, high wind speed
31.The table shows the average transpiration rates (cm³ per hour) for four plants with different leaf surface areas and stomatal densities. Which plant is likely to have the highest transpiration rate?
Hard
- APlant A: leaf area 100 cm², stomatal density 300 per mm²
- BPlant B: leaf area 150 cm², stomatal density 200 per mm²
- CPlant C: leaf area 80 cm², stomatal density 400 per mm²
- DPlant D: leaf area 120 cm², stomatal density 250 per mm²
32.Which of the following correctly describes the direction of transport in xylem and phloem?
Medium
- AXylem: unidirectional (roots to leaves); Phloem: bi-directional (source to sink)
- BXylem: bi-directional; Phloem: unidirectional (leaves to roots)
- CBoth are unidirectional from roots to leaves
- DBoth are bi-directional
33.In a potometer experiment, a student measures the distance moved by an air bubble over 5 minutes. The results are: without fan: 6 mm; with fan: 15 mm. What conclusion can be drawn?
Hard
- AWind speed increases transpiration rate because it removes water vapour from around the leaf.
- BWind speed decreases transpiration rate because it cools the leaf.
- CThe fan caused the bubble to move faster due to increased air pressure in the tube.
- DThe experiment is flawed because the bubble should move slower with a fan.
34.What is the main function of root hair cells in water absorption?
Easy
- ATo increase the surface area for absorption of water and mineral ions
- BTo carry out photosynthesis for the root
- CTo transport water to the xylem by active transport
- DTo store starch for the plant
35.Which of the following is not an adaptation of xylem vessels for transporting water?
Hard
- ACells are living and contain cytoplasm to actively pump water
- BCells are joined end to end without cross walls to form a continuous tube
- CCell walls are thickened with lignin for support
- DCells lose their organelles and become hollow
36.During winter, a deciduous tree has no leaves. Which part of the plant acts as the source for sucrose and amino acids transported in the phloem?
Medium
- AStorage organs in the roots
- BThe stem
- CThe branches
- DThe buds
37.What is the main function of xylem vessels in a plant?
Easy
- ATransport of water and mineral ions from roots to leaves
- BTransport of sucrose and amino acids from leaves to roots
- CTransport of water and mineral ions from leaves to roots
- DTransport of sucrose and amino acids from roots to leaves
38.Which of the following processes is involved in the loss of water from the leaves of plants?
Medium
- ADiffusion and evaporation
- BOsmosis and condensation
- CActive transport and evaporation
- DTranslocation and diffusion
39.A student collected some of the solution from the phloem in the stem of a plant. Which of the following would be present in the liquid?
Medium
- AAmino acids
- BStarch
- CCellulose
- DGlucose
40.Which of the following is an adaptation of xylem vessels for transporting water?
Easy
- ACells are dead with no cytoplasm, forming a continuous hollow tube
- BCells are living with thin walls to allow easy diffusion
- CCells have many chloroplasts to produce oxygen
- DCells contain sieve plates to allow flow of food

Slides

Xylem and Phloem

Plants have two transport vessels: xylem and phloem.
Xylem transports water and mineral ions from roots to leaves.
Phloem transports sucrose and amino acids from leaves to other parts.
They are arranged in groups called vascular bundles.

Which substance is transported by the phloem?

Water
Mineral ions
Sucrose and amino acids
Oxygen

Root Hair Cells

Root hairs are extensions of epidermal cells in the root.
They increase surface area for absorption.
Water enters by osmosis (soil water has higher water potential).
Mineral ions are absorbed by active transport.

How does water enter root hair cells?

Active transport
Diffusion
Osmosis
Transpiration

Pathway of Water

Water moves from soil into root hair cells.
Then across root cortex into xylem vessels by osmosis.
Transported up xylem to leaves, then into mesophyll cells.
Pathway: root hair cell → root cortex cells → xylem → leaf mesophyll cells.

Water moves from root hair cells to the ____ vessels in the centre of the root.

Transpiration

Transpiration is the loss of water vapour from leaves.
Water evaporates from mesophyll cell surfaces and diffuses out through stomata.
Xylem adaptations: cells dead, hollow, joined end-to-end, walls strengthened with lignin.
Water moves in one direction: roots to leaves.

What is transpiration?

Movement of water through xylem
Loss of water vapour from leaves
Uptake of water by roots
Transport of sucrose in phloem

Factors Affecting Transpiration Rate

High temperature increases transpiration (more evaporation).
High wind speed increases transpiration (removes water vapour).
High humidity decreases transpiration (less diffusion gradient).
Low humidity increases transpiration.

Which of these increase transpiration rate?

High temperature
High humidity
High wind speed
Low light intensity

Transpiration Stream (Extended)

Water molecules cohere, forming a continuous column in xylem.
Transpiration creates tension (pull) on water column.
Water is pulled up from roots to leaves.
Faster transpiration = faster water movement.

What property of water helps maintain the transpiration stream?

Adhesion
Cohesion
Surface tension
Specific heat capacity

Wilting (Extended)

Wilting occurs when water loss exceeds water uptake.
Cells lose turgor, plant cannot support itself and collapses.
Caused by insufficient soil water or high transpiration rate.

What causes a plant to wilt?

Too much water in soil
Water loss exceeds water uptake
High humidity
Low temperature

Translocation (Extended)

Translocation is the transport of sucrose and amino acids in phloem.
Phloem consists of living cells with sieve plates.
Substances move from source (where made) to sink (where used/stored).
Direction can change depending on season or growth stage.

Translocation moves ____ and amino acids through the phloem.

Comparing Xylem and Phloem

Xylem: dead cells, hollow, transports water/minerals one way (up).
Phloem: living cells, sieve plates, transports sucrose/amino acids in multiple directions.
Both are found in vascular bundles.

Which statements about xylem are correct?

Xylem cells are dead at maturity
Xylem transports sucrose
Xylem vessels have lignin
Xylem transports water in both directions

Which row correctly compares xylem and phloem?

Xylem: dead cells, transports water; Phloem: living cells, transports sucrose
Xylem: living cells, transports sucrose; Phloem: dead cells, transports water
Both are made of living cells and transport water
Both are made of dead cells and transport sucrose

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