Specific Learning Outcomes

1. a) Relate structures of the plant transport system to their functions in plants.
2. b) Illustrate arrangement of vascular tissues in monocotyledonous and dicotyledonous plants.
3. c) Demonstrate the uptake of water and mineral salts from roots to leaves.
4. d) Demonstrate factors that affect rate of transpiration in plants.
5. e) Describe translocation of manufactured food in plants.
6. f) Appreciate significance of transport in plants (examples from Kenyan crops such as maize, beans, tea).

1. What is Transport in Plants?

Transport in plants means movement of water, mineral salts and manufactured food (sugars) to parts where they are needed. Main transport systems: xylem (water & minerals) and phloem (manufactured food). These systems form vascular tissues found in stems, roots and leaves.

2. Structure of Transport Tissues and Their Functions

3. Arrangement of Vascular Tissues: Monocot vs Dicot

Drawings or cross-sections can be seen in stems and roots. Below are simple cross-section illustrations.

Note: In dicot roots the xylem often forms a central X (or star) with phloem between arms; in monocot roots vascular bundles are arranged in a ring with different patterns. Use maize and bean stems in class to compare.

4. Uptake of Water and Mineral Salts (From Roots to Leaves)

How water enters the root

• Root hairs: increase surface area to absorb water & dissolved salts.
• Pathways across cortex: apoplast (through cell walls), symplast (through cytoplasm via plasmodesmata) and vacuolar routes.
• Endodermis & Casparian strip: forces selective uptake into living cells (active transport) of minerals.

5. Transpiration — Loss of Water Vapour from Plants

Transpiration occurs mainly through stomata on leaves and also via cuticle and lenticels. Transpiration creates the pull that drives the upward movement of water in xylem.

Factors affecting rate of transpiration

• Light intensity: stomata open in light → increases transpiration.
• Temperature: warmer air increases evaporation and diffusion rate.
• Humidity: low humidity (dry air) increases transpiration; high humidity reduces it.
• Wind speed: removes humid air around leaf, increasing transpiration.
• Leaf surface area & stomatal number: larger area/more stomata = higher transpiration.
• Soil water availability: if soil dry, stomata close and transpiration falls.

Class demonstration ideas

1. Simple potometer experiment to measure rate of water uptake (use a cutting of bean or coleus). Diagram below shows the setup.
2. Compare weight loss (mass) of two potted plants—one covered with plastic bag (high humidity), one open—to show humidity effect.
3. Use blotting paper and fan to show wind effect on drying rate of leaf mimic.

6. Translocation of Manufactured Food (Phloem Transport)

Translocation moves sucrose and other solutes from sources (e.g., leaves) to sinks (e.g., roots, growing shoots, developing fruits/beans). The widely accepted explanation is the pressure-flow (mass flow) hypothesis:

1. Sugars are actively loaded into sieve tubes at the source (leaf), lowering water potential in the phloem.
2. Water enters sieve tubes by osmosis from nearby xylem, creating high pressure at source.
3. Sugars are removed at sink by active/unloading, water leaves, lowering pressure at sink.
4. Flow occurs from high pressure (source) to low pressure (sink) carrying dissolved food.

Phloem transport is bidirectional: different sieve tubes can move up or down depending on source-sink relationships (e.g. sugar leaves → root; stored starch in root converted to sugar to grow shoots in spring).

7. Significance of Transport in Plants

• Supplies water for photosynthesis, cell expansion and cooling by transpiration (important for crops like tea on highlands).
• Delivers mineral nutrients for growth and enzyme functions (e.g., nitrogen & potassium for maize & tea quality).
• Transports manufactured food to growing parts and storage organs (e.g., beans, tubers), critical for yield.
• Supports growth and repair by moving hormones and signalling molecules.
• Maintains plant turgor and structural support by continuous water columns.

8. Suggested Learning Experiences (Practical & Assessment)

1. Microscope: Observe prepared slides of xylem vessels and phloem sieve tubes; draw and label; compare features that suit their functions.
2. Field: Collect stem cross-sections from maize (monocot) and bean/sunflower (dicot). Make temporary slides or peel to show arrangement of vascular bundles.
3. Potometer practical: Measure transpiration in light vs dark, with a fan, and under a plastic bag; record and plot results; discuss variables and controls.
4. Uptake experiment: Use coloured dye in water to show movement up stem into leaves (cut sunflower or bean stems) — time how long before dye reaches leaves.
5. Investigation: Compare mass loss of potted plants (cover/leave uncovered) to demonstrate humidity & stomatal behavior.
6. Group activity: Explain how transport affects yield in a Kenyan crop (e.g., why poor root uptake reduces maize growth; how tea quality depends on translocation & leaf water status).
7. Assessment questions (examples):
• Explain how root structure enables absorption of water and mineral salts.
• Compare xylem and phloem structures and relate to their functions.
• Describe an experiment to show effect of wind on transpiration and how you would control variables.

Summary

Transport in plants depends on xylem (water & minerals) and phloem (food). Structures of these tissues suit their roles (dead, lignified xylem for strength and bulk flow; living phloem for active loading/unloading). Root hairs, osmosis and active transport enable uptake. Transpiration drives ascent of sap; factors like light, temperature, humidity and wind affect rates. Translocation moves sugars to growing and storage tissues — essential for plant growth and agricultural yields.