Chapter 9 Transport In Plants - Lecture Notes

Chapter 9: Transport in Plants Students should be able to: 1. 2. 3. 4. 5. 6. 7. 8. 9.

9.1

Relate structure and function of root hairs to their surface area, and to water and ion uptake. State transpiration as the loss of water from aerial parts of a plant, especially through stomata of the leaves. Describe how water loss is related to cell surfaces, air spaces and stomata. Describe effects of temperature, humidity and light intensity on transpiration rate. Describe wilting. Investigate the pathway of water using a suitable stain. Explain movement of water through the stem in terms of transpirational pull. Identify the position of the xylem and phloem as seen in the TS of a dicotyledonous stem and leaves. State the function of the xylem and phloem.

A Recap on Structure and Function of Root Hair Cells

Structure

Adaptation

Long and narrow

↑ SA: vol. Ratio ⇒ enhance rate of absorption of H2O and mineral salts Provide energy for active transport ⇒ by respiration Water enters by osmosis

Root hair cell is living 1. Cell sap conc. > Soil solution conc. 2. Cell sap is prevented from leaking out of root hair cell

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9.2

Transport & Vascular Tissue 9.2.1 Xylem Functions

Conduct water & mineral salts from roots  stem  leaves

Provide mechanical support for the plant

Structure

• • • •

Long, hollow tube from root to leaf Hollow space (lumen) is continuous Vessel is a dead structure Wall is strengthened by lignin

•

Does not hinder passage of water

•

Provide mechanical support to the plant

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9.2.2

Phloem

Function: Conduct manufactured food (sucrose & amino acids) from leaves to other parts of the plant Thin layer of cytoplasm

Cross-walls separating sieve tube cells

Make up the phloem

Living cells, provides energy required for active transport

Food moves by diffusion & active transport

9.3

Investigating Pathway of Water

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9.4.1

Internal structure of a dicotyledonous stem Cuticle prevents evaporation of water

Store food substances Phloem Cambium

Xylem •

9.4.2

Xylem + Phloem arranged in a ring

Internal structure of a dicotyledonous root Xylem

Phloem •

•

9.5 •

Xylem + Phloem lie on different radii, alternating with each other Epidermis is called a piliferous layer  no cuticle (Why?) (Hint: What is the role of the roots in a plant?)

Transpiration

Definition: The loss of water vapour from the aerial parts of the plant, especially through stomata of the leaves

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Water vapour loss from

9.5.1

Loss of H2O by plants Water moves out of mesophyll cells

Evaporate from surface of epidermal cell

Forming Thin film of moisture over surface of intercellular air spaces

Cuticular transpiration

Water evaporates out of intercellular air spaces

Water vapour goes out through stomata

Stomata Open

Stomata Closed

↑ Water Vapour Loss

↓ Water Vapour Loss

Impt of transpiration •

•

Suction force from transpiration pulls water & m.s from roots to leaves As water evaporates  cools the plant

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9.5.2

Factors affecting transpiration rate Note:

Transpiration Rate

↑ Humidity ⇒ ↑ amt of water vapour

Water Evaporation Rate

Humidity

↑ Humidity ⇒ ↓ transpiration rate

Temp. Of air

Wind condition

Light intensity

↑ L.I. ⇒ ↑ size of stomata ↑ Temp ⇒ ↑ transpiration rate

Windy external air Blow away water vapour

↑ Transpiration rate

WHY??

↓ Humidity

↑ Transpiration rate

9.6

Wilting

↑ Turgor pressure •

↑ Support of Leaf

Advantages of wilting  Cells lose ↓ water

Strong sunlight

↑ Transpiration rate

Cells lose water

↓ Turgor pressure

Stomata close

Cells become flaccid

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•

Disadvantages of wilting  When stomata closes  amt of CO2 entering leaf ↓  photosynthetic rate ↓ (since photosynthesis uses CO2)

9.7

Transpirational Pull

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