BIOLOGY SPM NOTES

1. TRANSPORT IN PLANTS
NAME : NOOR MELLINA BINTI ABU KASIM
CHAPTER : 1 - TRANSPORT (BIOLOGY FORM 5)
TEACHER : PUAN ZAHARAH BINTI THARIM
SCHOOL : SMKA (P) AL-MASHOOR

3. • 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

4. • 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

5. • 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

6. Figure : Cross section of dicotyledonous root

7. ::

8. • 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

9. Figure : Cross section of dicotyledonous stem

10. Figure : Cross section of monocotyledonous stem

11. • 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

12. Figure : Leaf
Figure : Cross section of leaf

13. • 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

14. Figure : Cross section of xylem

15. Figure : Tracheids
Figure : Xylem Vessel

16. • 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

17. • 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

18. • 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

19. • 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

20. Figure : Longitudinal section of phloem
Figure : Cross section of phloem

22. • 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

23. 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

24. 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

25. 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

26. • 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

27. • 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

28. • 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

29. • 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

30. • 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

31. 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

32. Figure : Movement of Water Through The Root

33. MOVEMENT OF WATER IN CORTEX AND ENDODERMIS
1. 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

34. :::

35. GUTTATION
1. At night, the roots of some small plants continue to actively transport ions and
water into xylem
2. This causes root pressure to increase
3. Transpiration rate is low during the night
4. 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 guttation
6. Guttation also occurs on cool humid mornings when the air is too saturated
for the water droplets to evaporate from the leaves

36. Figure : Leaf Guttation

37. MOVEMENT OF WATER THROUGH STEM
1. The continuous upward movement of water through the xylem vessels in the stems
can be attributed to capillarity
2. Capillarity / capillary action – results of the cohesive and adhesive forces which
enable water to enter and move along the very narrow columns
Water molecules adhere to one another by cohesive forces
Water molecules adhere to the walls of xylem vessels by adhesive forces
The cohesion and adhesion of water molecules are due to hydrogen bonding

38. 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

39. ::::;;:;;:

40. 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 saturated
3. 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

41. 7. Water from adjacent cell diffuses into the mesophyll cell by osmosis
8. Eventually, water is drawn from the xylem vessels in the veins
9. 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

42. Figure : Movement of Water from Leaves to
Atmosphere During Transpiration

43. • 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

44. Figure : Guard cells and Stoma

45. THE MECHANISM OF THE OPENING OF A STOMA
1. During the day, light stimulates photosynthesis in the guard cells
2. They start synthesizing glucose and generate energy for active transport
3. The guard cells accumulate potassium ions (K+) from adjacent cells through active
transport
4. The guard cells become hypertonic and water from the adjacent cells enter the
guard cells by osmosis
5. As a result, the guard cells swell up and become turgid
6. 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

46. Figure : Mechanism of The Opening of a Stomata

47. THE MECHANISM OF THE CLOSING
OF A STOMA
1. 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

48. • 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