IGCSE Biology - Transport in Plants

IGCSE Biology - Transport in Plants

• Plant Transport Systems: Plants have specialized tissues (xylem and phloem) for transporting water, mineral ions, and sugars.

• Xylem: Transports water and mineral ions from the roots to the rest of the plants. Xylem is unidirectional.

• Phloem: Transports sugars (primarily sucrose) produced during photosynthesis from sources (e.g., leaves) to sinks (e.g., roots, growing tissues). Phloem can transport in either direction.

• Root Hair Cells: Increase the surface area of the root, enabling efficient absorption of water and minerals from the soil.

• Transpiration: The loss of water vapor from leaves via the stomata.

• Factors Affecting Transpiration Rate:

  • Temperature: Higher temperatures increase transpiration.
  • Humidity: Lower humidity increases transpiration.
  • Wind Speed: Higher wind speed increases transpiration.
  • Light Intensity: Higher light intensity usually increases transpiration if stomata are open.
  • Stomatal Density: The number of stomata affects the overall rate.

• Transpiration Stream: The movement of water through the xylem driven by transpiration pull.

• Potometer: A laboratory apparatus used to measure the rate of transpiration.

• Translocation: The movement of sugars (sucrose, amino acids) through the phloem. This can occur in both directions.

• Source: Location where sugars are produced or loaded into the phloem.

• Sink: Location where sugars are used or stored.

• Adaptations of Xylem Vessels:

  • Hollowed out cells to minimize resistance to water flow.
  • Lignified walls for support and to prevent collapsing under tension.
  • Pits allow water to move through laterally between cells.

• Adaptations of Root Hair Cells:

  • Large surface area to increase water absorption.
  • Thin walls to facilitate osmosis.

• Effect of Root Hairs: Root hairs maximize absorption of water and mineral ions by increasing the surface area of the root system.

• Pathway of Water Absorption: Water travels from soil, through root hair cells, across the cortex, through the endodermis and vascular tissue to the xylem.

• Water Uptake: Driven mainly by osmosis.

• Minerals Uptake: Via diffusion driven by concentration differences.

• Types of transport in plants: Passive transport includes osmosis , active transport involves ATP energy to move substances against a concentration gradient.

• Water Loss and Wilting: Causes include high temperatures and low water availability. Wilting is a visible sign of insufficient water.

Example Questions and Answers (from the provided documents)

• What has caused the plant's appearance to change?

  • Water loss by transpiration greater than water uptake.

• Which order below is correct in describing the pathway of water as it travels from the roots through a plant?

  • Root hair cell → xylem→ mesophyll cells → xylem → stomata

• Which of the following is a correct explanation of the process of translocation in a plant?

  • The movement of sucrose and amino acids through the phloem from a source to a sink.

• Processes involved in water loss

  • Diffusion
  • Evaporation

• What is a potometer?

  • A device used to measure transpiration rate.

• How can temperature affect transpiration?

  • Higher temperatures increase transpiration rates

• Correctly Labelled regions for plant diagram -Regions 1 and 3 (for root)

  • Regions 1 and 4 (for stem)

• Which environmental factor is most likely to be responsible for a plant to wilt?

  • A decrease in the amount of available water.