CLASS: SS3

SUBJECT: BIOLOGY                                                    PERIOD(S) 3

TOPIC: MECHANISM OF TRANSPORT IN HIGHER PLANTS

SUBTOPIC 1: TRANSLOCATION AND TRANSPIRATION

SUBTOPIC 2: WATER ABSORPTION AND TRANSPORT

SUBTOPIC 3: DIFFERENCES IN PLANT AND ANIMAL TRANSPORT

PREVIOUS KNOWLEDGE: Students are familiar with the topic

 

OBJECTIVES: At the end of the period

  1. Students should be able to:

PERIOD 1:

  1. Discuss the mechanism of transportation in plants
  2. Describe the tissues involved in the transportation of material

PERIOD 2:

  1. Explain how manufactured food, water, mineral salts, and other materials are transported in plants.

PERIOD 3:

  1. List the differences between transport in plants and animals.
  2. Demonstrate experimentally the flow of materials in plants

REFERENCES:

Essential Biology for Senior Secondary Schools by M.C Micheals pg 292 – 300

Modern Biology for senior secondary schools pg 312 – 317

 

CONTENT

In a simple plant (algae), materials enter or leave the body cells by diffusion (gases) manufactured food and waste products) and water enters by osmosis. In higher land plants, vascular tissues (special conducting tissues) carry out transport with latex tubes to assist. The major materials transported in plants are gases (CO2 and O2), water, mineral salts, manufactured food, nitrogenous waste products, hormones and pigments. Plant saps, cell sap and cytoplasm are the main transport media. Gases are mainly absorbed through the stomata (in the leaves) and lenticels (in the stem).

         

Water and mineral salts are absorbed through the root system, water, mineral salts and soluble food are transported in the vascular tissues of the plant. The vascular tissue are made up of a network of long tubes called vascular bundles. A vascular bundle consists of the xylem and phloem tissues. The cambium exists between the xylem and phloem tissues in the roots and stems of dicotyledonous plants.

  1. Cambium – are made up of narrow living cells with thin walls and dense cytoplasm. Cambium produce secondary xylem and phloem by dividing and multiplying. This growth in width (girth) of the stem is called secondary thickening.
  2. Xylem tissues – consists of dead cells with lignified cell walls. Xylem transport water and dissolved mineral salts from the roots to other plant parts. It also give support and rigidity to plants.

iii.      Phloem: Consists of thin walled living cells with dense cytoplasm which have perforated cross walls. Phloem transports a manufactured food from the leaves to other plant parts.

 

TRANSLOCATION

This is the process by which manufactured food is transported from green leaves of a plant to all the living plant cells especially those in the actively growing regions (root tips, stem tips and buds) and excess food is also stored. Phloem is responsible for this. Glucose, oil, resin, protein, alkaloids and hormones are among the translocated materials.

 

TRANSPIRATION

Transpiration is the loss of water from the leaf surface of plants by evaporation. The continuous flow of water from the roots to the leaves is called the transpiration stream. Plants loose excess water through the stomata (stomata transpiration), lenticels (lenticular transpiration) and the leaf cuticle (cuticular transpiration). Transpiration is affected by the following factors:

  1. Temperature – increase in temperature causes increase in transpiration rate
  2. Wind – increase in wind causes increase in transpiration

iii.      Soil water-high level of soil water results in higher absorption and transpiration rate.

  1. Light – High light intensity results in high photosynthetic rate leads to increase in temperature and therefore, increase in transpiration.
  2. Humidity: Higher humidity leads to reduce rate of transpiration and vice versa.
  3. size of stomata pores – when the guard cells become turgid and the stomata open leading to transpiration however when the guard cells are flaccid, the stomata close and transpiration stops.

 

WATER ABSORPTION BY PLANT ROOTS

The cell sap in the root hairs is more concentrated than the soil water. The cell membrane of the root hairs is selectively permeable therefore, soil water enters the vacuole of the root hairs via osmosis. The extra water causes increase in tugor pressure of the vacuole (reduce osmotic pressure) and forces water out into the cell walls towards the cortex. The cell next to the root hair on the inside has a lower turgor (higher osmotic pressure) hence water will pass into it by osmosis. This process enables water absorbed to get to the xylem vessels.

 

TRANSPORT OF WATER IN THE XYLEM TISSUE

Water transport by the xylem is due to the following process

  1. Capillary action: This allows the upward movement of water through the xylem from the roots to the leaves. The xylem vessels form very fine capillary tubes.
  2. Root pressure and suction pressure – Osmotic pressure difference between the cell sap and soil nutrients concentration create root pressure. The cell sap becomes more concentrated and it tends to draw up the nutrients. Suction pressure occurs during stomata transpiration. This pressure facilitates the movement of water from the soil to the xylem tissues.

 

iii.      Transpiration stream or pull

 

SIMILARITIES IN TRANSPORT IN ANIMALS AND PLANTS

  1. A liquid medium is required
  2. Materials are transported in dissolved form.
  3. Tabular or cylindrical vessels are necessary
  4. Diffusion and Osmosis play key roles in transportation

 

 

 

DIFFERENCES BETWEEN PLANTS AND ANIMALS

 

PLANTS

ANIMALS

1

Media from transportation is cell sap

Blood is the medium of transportation `

2

Root pressure or transpiration generates forces for pull

Heart generates forces for transport of nutrients.

3.

The transport medium is not tissue

Transport medium is made up of cells of different types of tissues.

4.

Materials are transported through different vessels (xylem and phloem)

Materials are transported in the same vessels(blood vessels)

 

INSTRUCTIONAL MATERIALS – PICTURES AND VIDEOS ON TRANSPORTATION INPLANTS

TEACHING METHODS PROCEDURES

Step 1: Teacher revises the previous topic and introduce the new topic

Step II: Teacher explains how materials get transported in plants.

Step III: Teacher explains absorption of water and mineral salts by the root hairs.

Step IV: Teacher lists the differences between transportation in plants and animals.

Step V: Teacher allows students to ask questions and writes notes under content on the board.

 

CLASSWORK (ACTIVITIES)

PERIOD 1: Students discuss transportation of materials in higher plants

Period 2: Students discuss the vessels of transportation and how they carry out their functions

Period 3: Students list the differences in plants and animal transport.

 

EVALUATION

PERIOD I: Explain transport in higher plants

PERIOD 2: State the function of

  1. Xylem
  2. Phloem

PERIOD 3: List 3 factors affecting transpiration

 

SUMMARY/CONCLUSION: Teacher summarizes the topic, marks the notes of the students and make corrections where necessary.

 

ASSIGNMENT(S)

  1. Describe an experiment to show the translocation occurs through the phloem tissue.
  2. Describe an experiment to demonstrate transpiration in plants.
  3. Describe an experiment to show that water is conducted in the xylem tissue of flowering plants.
  4. Describe an experiment to demonstrate root pressure and transpiration pull.