Transport In Plants

边玩边学

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课程笔记

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.

Vascular tissue in a dicotyledonous plant

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.

Structure of the root and root hair cells

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.

Pathway of water into and across a root

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.

Transpiration in plants

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.

A wilted plant

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.

Potometer apparatus

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.

Translocation through the phloem

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练习题

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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?
Easy
- 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?
Medium
- 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?
Easy
- AWater and mineral ions
- BSucrose and amino acids
- COxygen and carbon dioxide
- DStarch and cellulose
7.Evaporation of water, which contributes to transpiration, occurs from the surface of which leaf structure?
Medium
- 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

更多题目

9.Which adaptation of xylem vessels allows for the continuous flow of water?
Medium
- 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?
Medium
- ALeaves
- BStorage organs (e.g., roots)
- CStems
- DFlowers
13.The table shows data from four plants growing under the same conditions. | Plant | Leaves | Avg leaf area (cm²) | Stomatal density (per mm²) | Stoma diameter (μm) | |---|---|---|---|---| | A | 36 | 53 | 276 | 19 | | B | 21 | 51 | 247 | 18 | | C | 24 | 45 | 249 | 15 | | D | 17 | 40 | 151 | 16 | Which plant will have the lowest rate of transpiration?
Hard
- APlant A
- BPlant B
- CPlant C
- DPlant D
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?
Medium
- 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:
Medium
- 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?
Medium
- 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.In a root, which tissue is responsible for transporting water up to the stem?
Easy
- 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?
Medium
- 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.In a cross-section of a dicotyledonous stem, which position corresponds to the phloem?
Easy
- AThe outer ring of cells, just inside the epidermis
- BThe ring of cells with thick walls, towards the centre
- CThe central pith region
- DA single layer of cells surrounding the stem
28.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
29.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
30.The table shows the leaf area and stomatal density for four plants. | Plant | Leaf area (cm²) | Stomatal density (per mm²) | |---|---| | A | 100 | 300 | | B | 150 | 200 | | C | 80 | 400 | | D | 120 | 250 | Which plant is likely to have the highest rate of transpiration?
Hard
- APlant A
- BPlant B
- CPlant C
- DPlant D
31.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?
Medium
- 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.
32.Which of the following is not an adaptation of xylem vessels for transporting water?
Medium
- 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
33.Which of the following processes is involved in the loss of water from the leaves of plants?
Easy
- ADiffusion and evaporation
- BOsmosis and condensation
- CActive transport and evaporation
- DTranslocation and diffusion
34.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
35.Which of the following is an adaptation of xylem vessels for transporting water?
Medium
- 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
36.Xylem vessels are made of living cells.
Easy
True or false?
37.Which substance is deposited in the walls of xylem vessels to strengthen them?
Easy
- ACellulose
- BLignin
- CSuberin
- DChitin
38.Root hair cells absorb water from the soil by which process?
Easy
- AActive transport
- BDiffusion
- COsmosis
- DTranspiration
39.Phloem transports water and mineral ions from roots to leaves.
Easy
True or false?
40.In a dicotyledonous stem, where is the xylem located relative to the phloem in a vascular bundle?
Easy
- AXylem is on the outside, phloem on the inside
- BXylem is on the inside, phloem on the outside
- CXylem and phloem are mixed together
- DXylem surrounds the phloem
41.Which of the following is an adaptation of xylem vessels for water transport?
Easy
- AThey contain cytoplasm to pump water
- BThey have cross walls to regulate flow
- CThey are hollow and lack cell contents
- DThey have sieve plates for easy flow
42.Increasing wind speed decreases the rate of transpiration.
Easy
True or false?
43.In a potometer experiment, which factor is kept constant to ensure a fair test when investigating the effect of temperature?
Medium
- AWind speed
- BLight intensity
- CBoth wind speed and light intensity
- DThe type of plant
44.Which statement explains why water moves up the xylem vessels against gravity?
Medium
- AActive transport in xylem cells pushes water upwards
- BRoot pressure forces water into the xylem
- CCohesion between water molecules and transpiration pull from leaves
- DOsmosis creates a pressure gradient in the stem
45.In winter, when a deciduous tree has no leaves, the roots act as a source for sucrose and amino acids transported in the phloem.
Medium
True or false?
46.Complete the sentence.
Easy
The loss of water vapour from plant leaves is called ____.

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