biology form 5 chapter 1.7 & 1.8 (transport in plants)
TRANSCRIPT
TRANSPORT IN PLANTS
NAME : NOOR MELLINA BINTI ABU KASIMCHAPTER : 1 - TRANSPORT (BIOLOGY FORM 5)TEACHER : PUAN ZAHARAH BINTI THARIMSCHOOL : SMKA (P) AL-MASHOOR
1.7 UNDERSTANDING THE TRANSPORT OF SUBSTANCES IN PLANTS
• Vascular tissue : Transport substances in plants• There are 2 types of vascular tissue : xylem &
phloem• Xylem : - Transport water and dissolved
mineral salts absorbed by the roots up the stems and to the leaves
- Provides mechanical support to woody plant• Phloem : Transport organic substances from
leaves down to the storage organs and from the storage organs (roots) up to the growing regions (buds)
• Vascular tissues are found in the roots, stems and leaves of a plant
VASCULAR TISSUE
VASCULAR TISSUE IN ROOT
• Outermost layer of root : Epidermis - No waxy cuticles
- Absorbs water and dissolved
mineral ions from soil• Specialised epidermal cells grow outwards to
form root hairs• Root hair – Increase the surface area for water absorption• Cortex - Region between the epidermis and vascular cylinder
- Made up of parenchyma cells which stores starch grain• Endodermis – Single layer of cells located
immediately after the cortex
• Pericycle - Next to endodermis - Consist of sclerenchyma tissue :
Provides mechanical support for the roots
• Vascular cylinder : Consist of vascular tissue and pericycle
• In dicotyledonous plant : Xylem has a star-shaped form, phloem fills the areas between the xylem
• In monocotyledonous plant : - Vascular cylinder has a central core called pith which contain parenchyma cell
- Vascular tissues form a ring around the pith, xylem tissue alternating with phloem tissue
Figure : Cross section of dicotyledonous root
::
VASCULAR TISSUE IN STEM• Stem has epidermal layer : - Epidermal layer secrete
cuticle (in young plant) - Epidermis absent but is replaced by bark (in older plant)
• Cortex layer : Inside epidermis• Cortex layer is made up of : - Collenchyma cells :
provide support and flexibility to stem - Parenchyma cells : store food • Inner part of stems consist of vascular bundles and pith
which is the central region of stem• Pith : - Used for food storage in young plants - May be absent in older plant, making them hollow• Vascular bundle : - In dicotyledonous plants : - Arranged in
ring around the pith - Xylem are
found towards inside with the phloem on the outside. Cambium lies between
xylem and phloem - In monocotyledonous plants :
Scattered throughout the stem
Figure : Cross section of dicotyledonous stem
Figure : Cross section of monocotyledonous stem
VASCULAR TISSUE IN LEAF
• The leaf consist of broad portion called lamina (leaf blade)
• Leaf blade (lamina) : Contains leaf veins• Petiole : Stalk that connects the leaf blade to
the stem• Vascular tissue : Found inside petiole and leaf
veins• Xylem : - Forms upper part of vascular bundle
in leaf - Transport water and mineral salts to
the leaves• Phloem : - Forms lower part of vascular bundle
in leaf - Transport sucrose and other products
of photosynthesis from leaves
Figure : Leaf
Figure : Cross section of leaf
STRUCTURE OF XYLEM
• Xylem contains 4 types of cells : - Xylem vessels
- Tracheids - Fibres (a type of
sclerenchyma) - Parenchyma
• Xylem vessels & Tracheids : water-conducting cells• Fibres : Provide support to the xylem• Parenchyma : Stores food substances
Figure : Cross section of xylem
Figure : TracheidsFigure : Xylem Vessel
ADAPTATION OF XYLEM VESSELS & TRACHEIDS
• They are elongated cells arranged end to end- The end walls of xylem vessels are open so that the
cells join end to end to form a long continuous hollow tube
- This arrangement allows water to flow upwards continuously from one cell to the next• During growth, the walls of the xylem vessels and
tracheids are thickened with lignin deposits- Lignin : - Making them strong & hardy so that they do
not collapse under the tension created by the upward pull of water during transpiration (transpiration pull)
- Prevent the entry of food substances. Hence, cytoplasm of these cells are disintegrates, leaving a cavity in the centre of the cells. As a result, mature xylem vessels and tracheids are hollow and dead
• The walls of xylem vessels and tracheids have small openings (pits)
- Pits : Allow water and mineral salts to pass sideways between the cells
TRACHEIDS
• Longer and have smaller diameter than xylem vessels
• They are pointed at the ends
• The end walls break down in the pits to allow water to pass from cell to cell
STRUCTURE OF PHLOEM
• Phloem tissue is composed of 4 types of cells : - Sieve tubes - Companion cells - Parenchyma - Fibres
• Sieve tubes : - Transport for organic substance such as sucrose and amino acids
- Sieve tube is a cylindrical column comprising long cells arranged end to end
- When mature, it has no nucleus and its cytoplasm is pushed to the sides of the cell
- The end walls of each cell are perforated by pores to form sieve plate. Long strands of cytoplasm pass through the pores in the sieve plates to allow substances to pass from one cell to another
- Its function is supported by companion cells
• Companion cells : - Normal cell with a nucleus and a large number of mitochondria
- Has active metabolism - Provide sieve tube cells with
protein, ATP, and other nutrients
• Parenchyma : Store food substances
• Fibres : Provide support
Figure : Longitudinal section of phloem
Figure : Cross section of phloem
1.8 THE TRANSPORT OF ORGANIC SUBSTANCES AND WATER IN PLANTS
TRANSPORT OF ORGANIC SUBSTANCES IN PLANTS
• Phloem contains a very concentrated solution (phloem sap) of dissolved organic solutes such as sugars (sucrose), amino acids and other metabolites
• Translocation : Transport of dissolved organic solutes in phloem
• Importance of translocation : - For the survival of plant
- Enables sucrose, product of photosynthesis, to be stored / converted into other sugars when it
reaches its destination• Organic substances in phloem can be
transported both upwards and downwards
TRANSPORT OF WATER IN PLANTS
TRANSPIRATION• Transpiration : Loss of water vapour through
evaporation from the surface of plants• This loss of water is replaced by the absorption of
water from soil by plant roots• Only 1% of water is used for photosynthesis and
to remain turgid• 99% of water is evaporates from leaves and is lost
to the atmosphere through transpiration• Transpiration takes place through stomata of
leaves and lenticles of woody stems• Transpiration stream : Continuous stream of
flowing of water from roots to leaves
IMPORTANCE OF TRANSPIRATION
• Helps in absorption and transport of water and mineral ions from roots to different parts of the plant
• Produce cooling effect in plants
• Helps to supply water to all plant cells for metabolic processes
• Helps to prevent plants from wilting by maintaining cell turgidity
EXTERNAL CONDITIONS THAT AFFECT THE RATE OF TRANSPIRATION
• Light intensity- An increase in light intensity increases the
rate of transpiration- Light stimulates the opening of stomata- The stomata will open wider- Hence, more water vapour evaporates
through stomata
• Temperature- An increase in temperature increases the rate of transpiration- An increase in temperature increases the rate of evaporation of water from surface of mesophylls cell- The rate of diffusion of water through stomata
also increases
• Humidity- High humidity surrounding the leaves reduces the evaporation of water from the stomata - This causes the transpiration to slow
down- Conversely, a rise in temperature lowers the relative humidity of the surrounding
air and this increases the rate of transpiration
• Air movement- As the water vapour that diffuses
through the stomata accumulates near the leaf surface, a faster air movement helps to remove the water vapour- Air movement increases the
concentration gradient between the water vapour in
the leaf and that outside leaf- This increases the transpiration rate- When the air is still, the transpiration
rate decreases or stops altogether
MOVEMENT OF WATER FROM SOIL TO LEAVES
• Movement of water from the roots to the leaves is assisted by :
- Root pressure- Capillary action- Transpiration pull
• Water is absorbed through roots by osmosis• The gradient of water concentration which exist
across the cortex creates a pushing force that results in the inflow of water into the xylem
• At the same time, ions from the soil are actively secreted into the xylem and this causes osmotic pressure to increase
• As a result, water flows continuously into the xylem. This generates a pressure known as root pressure
• Root pressure results in an upward push of water and mineral ions into the xylem of the stem
• Root pressure causes an upward movement of water in plants but it is insufficient to overcome the force of gravity to push the water upwards to the maximum heights of many trees
• Hence, the upward movement of water through the xylem vessels in the stem is helped by the adhesive and cohesive properties of the water molecules
MOVEMENT OF WATER THROUGH THE ROOTS
1. The cytoplasm of root hair cells is usually hypertonic to the surrounding soil water
2. This means that root cells have a higher concentration of solutes than the water in the surrounding soil
3. Hence, water enters the root hair cells via osmosis
4. The root hair cell is now hypotonic to the adjacent cells
5. Water then diffuses into the adjacent cells by osmosis
6. In this way, water moves inwards from cell to cell in the cortex until it reaches the xylem vessels in the root
Figure : Movement of Water Through The Root
MOVEMENT OF WATER IN CORTEX AND ENDODERMIS1. Water flows through cytoplasm, vacuoles and cell
walls of the parenchyma cells in the cortex until it reaches the endodermis
2. Once it reaches the endodermal cells, the water moves through the cytoplasm and vacuoles instead of the cell walls
3. This is because the endodermal cells have special features called Casparian strips which line the sides of the endodermal cells
4. Casparian strip : Impermeable to water (block the movement of water through cell wall)
5. Instead, water moves from cytoplasm and vacuole in the endodermal cells to the xylem cells
:::
GUTTATION1. At night, the roots of some small plants
continue to actively transport ions and water into xylem
2. This causes root pressure to increase3. Transpiration rate is low during the night4. Root pressure can push water all the way up
the stem and out of special pores called hydathodes at the edge of leaves
5. This natural process is called guttation6. Guttation also occurs on cool humid mornings
when the air is too saturated for the water droplets to evaporate from the leaves
Figure : Leaf Guttation
MOVEMENT OF WATER THROUGH STEM1. The continuous upward movement of water through the
xylem vessels in the stems can be attributed to capillarity2. Capillarity / capillary action – results of the cohesive and
adhesive forces which enable water to enter and move along the very narrow columnsWater molecules adhere to one another by cohesive forcesWater molecules adhere to the walls of xylem vessels by adhesive forces
The cohesion and adhesion of water molecules are due to hydrogen bonding
3. Xylem vessels - Long, narrow and hollow tubes - Joined end to end to form continuous column of water
from the roots to the leaves through the stems 4. The narrow xylem vessel increases the force generated by capillarity.
Capillary action holds the water column together in the capillary-sized xylem vessel
5. Although root pressure and capillary action are not enough to carry water to the top of a tall tree, both effects are important to the water movement in plants
::::;;:;;:
1. The water on the external surfaces of the mesophyll cells evaporates, saturating the air spaces in the mesophyll with water vapour
2. The air in the atmosphere is less saturated3. So, the concentration of water vapour in
atmosphere is lower than the concentration of water vapour in air spaces of the leaf
4. Hence, water vapour in the air spaces evaporates and diffuses through the stomata
5. The movement of air carries the water vapour away from stomata
6. The loss of water in mesophyll cells makes the cell hypertonic to an adjacent cell
MOVEMENT OF WATER FROM LEAVES TO ATMOSPHERE
7. Water from adjacent cell diffuses into the mesophyll cell by osmosis
8. Eventually, water is drawn from the xylem vessels in the veins9. A tension and pulling force is created to pull water up the
xylem vessels as a result of the evaporation of water vapour from the mesophyll cells
10.This transpiration in the leaves forces the movement of water from soil up the stem
11.The pulling or suction force is known as a transpirational pull
Figure : Movement of Water from Leaves to Atmosphere During Transpiration
THE REGULATION OF TRANSPIRATION BY STOMATA
• The regulation of transpiration in plant is helped by the opening and closing of stomata
• Stomata are found abundantly on the lower epidermis of dicotyledonous leaf and on both upper & lower surfaces of monocotyledonous leaf
• Each stoma is surrounded by two guard cells which regulate gaseous exchange by opening and closing the stoma
• If the stomata are open - Carbon dioxide can enter for photosynthesis
- Water can be lost by transpiration• If the stomata are close - Reduce water loss (stops
transpiration) - Prevents carbon dioxide from
entering the leaf• In general, stomata open during the day and close at
night
Figure : Guard cells and Stoma
THE MECHANISM OF THE OPENING OF A STOMA1. During the day, light stimulates photosynthesis in
the guard cells2. They start synthesizing glucose and generate
energy for active transport3. The guard cells accumulate potassium ions (K+)
from adjacent cells through active transport4. The guard cells become hypertonic and water from
the adjacent cells enter the guard cells by osmosis5. As a result, the guard cells swell up and become
turgid6. Since the inner cell walls of the guard cells are
thicker than the outer cell walls, the guard cell bend outward an the stoma opens. This is because the thinner outer wall stretches more than the thicker inner wall
Figure : Mechanism of The Opening of a Stomata
THE MECHANISM OF THE CLOSING OF A STOMA1. At night, when
photosynthesis does not take place, potassium ion (K+) exit the guard cells and water also leaves the guard cells by osmosis
2. The guard cells become flaccid and the stoma closes
Figure : Mechanism of The Closing of a Stomata
SUMMARY
•Vascular tissues transport substances in plant- Xylem : Transport water and dissolved minerals- Phloem : Transport organic substances (translocation)
•Transpiration is the loss of water vapour from surfaces of plants through evaporation
- Affected by light intensity, temperature, humidity and air movement•Movement of water from roots to leaves is assisted by root pressure, capillary action and transpirational pull•The opening and closing of stomata help in regulation of transpiration in plant
THE END