Growth Curves

  • Will learn about the organisation of plant tissue, meristematic tissues dan growth and growth curve.

Organisation of Plant tissue

Plant tissue
Meristematic tissue Permanent tissue
  • Apical meristamic tissues
  • Lateral meristamatic tissues
  • Epidermal tissues
  • Ground tissues:
    •          Parencyhma tissues
    •          Collenchyma tissues
    •          Sclerencyma tissues
  • Vascular tissues:
    •          Xylem tissues
    •          Phloem tissues

Types of permanent tissues and their functions:


1. Epidermal tissues:

  • Epidermal tissues layer the outermost surface of stems,leaves and roots of young plants.
  • Epidermal cell walls which are exposed to the air have a waxy and waterproof layer called cuticle.
  • The cuticle reduces loss of water through evaporation (transpiration), protects the leaf from mechanical injuries and pathogens.

2. Ground tissue:

a)   Parenchyma tissues
  • Paracenchyma tissues are simplest living cells and do not undergo differentiation.
  • They have the thinnest cell walls.
  • Parenchyma tissues are always in a turgid state providing support and maintaining the shape of herbaceous plants.
  • Involved in photosynthesis,help in the storage of starch and sugar and involved in gaseous exchange.
  • Involved in the repair and regenaration of plant tissue as well as in the vascular system.
b)   Collenchyma tissues
  • Collenchyma tissues are made of living cells which mature into cells that are flexible.
  • Have cell walls made of pectin and hemicellulose.
  • Their cell walls are thicker than parenchyma tissues.
  • Provide mechanical support and elasticity to plants.
c)   Sclerenchyma tissues
  • Sclerenchyma tissues consist of dead cells when they are matured.
  • Their cell walls are the thickest among the three ground tissues.
  • Provide support and mechanicak strength to the parts of matured plants.These tissues also help in the transport of water and nutrients in plants.

3. Vascular tissue:

a)   Xylem
  • Xylem is made up of dead cells without cytoplasm
  • The cell wall of xylem contains lignin.
  • Consists of xylem vessels that are elongated,hollow and connected to each other from its roots to the leaves.
  • This enables xylem to tarnsport water and mineral salt to all parts of a plant.
b)   Phloem
  • Phloems are made of companion cells and sieve tubes.
  • Made of living cells, which is the sieve tubes with the presence of cytoplasm.
  • The sieve tubes do not have organelles such as nucleus and ribosome as they decompose at maturity stage.
  • Phloems consist of sieve tubes arranged from end to end froming elongated and continuos tube structures.
  • Phloems transport sugars produced from the photosynthesis from the leaves to storage organs such as roots,fruits and      tubers.

Meristematic Tissues and Growth

  • Zone of cell growth:-
Zone of cell divison
  • The zone of cell division takes place at the apical meristems
  • The increase of the number of cells causes the elongation of the plant stem
  • When the new cells are forming, the cells formed previously are pushed to the zone of cell elongation.
Zone of cell elongation
  • The zone of cell elongation consists of cells that are increasing in size.
  • Happens through water diffusion by osmosis and the absorption of nutirents into the cells and stored in the vacoule.
  • Small vacoules fuse to form a large vacoule through vacuolation.
  • The diffused water exerts pressure against the cell wall which pushes, elongates and widens the cells.
Zone of cell differentiation
  • The zone of cell differentiation consists of differentiating cells that differentiate once they have reached their maximum size.
  • Cells differentiate to form permanent tissues such as epidermis,cortex,xylem and phloem.
  • The cells change their shapes and structures to become specialised cells with specific functions.
  • Types of growth:
a)   Primary growth:
  • Primary growth is the growth that occurs after germination and it takes place in all plants to elongate their stems and roots.
  • Takes place in the apical meristems at the shoot tips and root tips.
  • At the shoot tips, leaf primordia and shoot primodia will grow to form new leaves and shoots.
  • Enables plants to increase in height.
  • At the root rips, the root cap will become exhausted when they penetrate the soil.
  • Root cap to be replaced by the meristem cells.
b)   Secondary growth:
  • Secondary growth occurs mainly in eudicots and a small number of monocots (shrub) to increase the circumference or diameter of plant stem and root
  • Lateral meristems consists of vascular cambium (located between phloem and xylem tissues in vascular bundles) and cork cambium (located under the epidermal layer).
  • Secondary growth at the stem:
  1. Secondary growth starts when the vascular cambium divides actively through mitosis.
  2. The cells in the cambium ring divide inwards to form new xylem and outwards to form new phloem. The new xylem tissues become secondary xylem and the new phloem tissues become secondary phloem.
  3. When undergoing secondary growth, primary xylem is pushed towards the pith whereas primary phloem is pushed towards the epidermis.
  4. As a result, the primary xylem tissues are compressed to form a stronger wood layer.
  5. When the secondary xylem layer is compressed,there is an addition to the circumference of the stem which causes the epidermis of the stem to strecth and crack.                                       
  6. Cork cambium actively divides to form cork cells on the outer side and cortex on the inner side.
  • Secondary growth at the root:
  1. Vascular cambium cells divide actively and combine to form a complete ring.
  2. The cells in the cambium ring divide inwards to form secondary xylem and outward to form secondary phloem.
  3. Due to vascular cambium activity, the root becomes thicker.
  4. The cork cambium located under the epidermis divides actively to form cork cells. The cork cells provide protection to the root tissues.
  • The necessity of plants' growth
The necessity of primary growth
  • Allow the maximum elongation of plants to absorb sunlight for photosynthesis.
  • Primary phloem can transport the products of photosynthesis from the leaves to other parts of the plants.
  • Primary xylem can transport water and mineral salts form the soil via the roots to the leaves.
  • Primary xylem provides support to herbaceous or young plants.
The necessity of secondary growth
  • Provides stability to plants by increasing the stem and root diameters to suit the height of plants.
  • Provides mechanical support to plants.
  • Produces more xylem and phloem tissues.
  • Produces xylem and phloem tissues continuosly to replace old and damaged xylem and phloem tissues.
  • Produces stronger and thicker bark to provide protection to the plants.
  • Able to live longer by increasing the chances of seed production and reproduction.
  • Comparison between primary growth and secondary growth in eudicots
Similarities between primary growth and secondary growth in eudicots:
  • Both growths can increase the size of plants permanently
  • Both growths occur in woody plants.
  • Both growths involve cell division by mitosis.
Differences between primary growth and secondary growth in eudicots
Aspect Primary growth 
Tissue Involved Apical meristem
Parts of plant  Occurs on stems and roots in younger region of plants
Direction of growth Growth occurs longitudinally
Growth effect Increases the length of stems and roots of plants
Tissue formed Epidermis,cortex,primary vascular tissues (primary xylem and primary phloem)
Woody tissue Absence
Bark thickness Thin
Annual growth ring Absence
Aspect Secondary growth
Tissue Involved Lateral meristem (vascular cambium and cork cambium)
Parts of plant  Occurs when primary growth has ceased on matured stems and roots.
Direction of growth Growth occurs radially
Growth effect Increases the thickness or circumference of stems and roots of plant
Tissue formed Bark,periderm (cork cambium and cork tissues),lenticels and secondary vascular tissues (secondary xylem and secondary phloem).
Woody tissue Presence
Bark thickness Thick
Annual growth ring Presence
  • Plants that undergone secondary growth are important in terms of economy due to the woods:
  • Timber has great economic value for wood industry
  • Types of tree which have great economic value for wood industry are merbau,jati,cengal,akasia,rubber and meranti trees
  • The trees that are hard and tough can be used in construction and furniture sectors
  • Akasia and batai can be used to produce paper
  • Merawan and meranti can be used to produce oils
  • Hibiscus and bougainvillea plants are used as long-lived plants

Growth Curves

  • Types of plants based on their life cycles:
Annual plants:
  • Annual plants are plants that have only one life cycle for a season or a year.
  • These plants usually die after produce flowers and fruits.
  • Examples: maize,mustard greens,tomatoes and onions.
Biennial plants:
  • Biennial plants are plants that ended their life cycle in two years by two growing systems.
  • First year is the phase of vegetative, which is the growth of leaves and stems structures.
  • At the second year, the plants produce flowers and fruit.
  • Examples; tulip plants,spinash and cabbages.
Perennial plants:
  • Perennial plants are the plants which can live longer although after the formation of flowers and fruits.
  • All the perennial plants are woody plants.
  • These plants can continue to live as long as do not infected by diseases or destroyed by humans,animals or disasters.
  • Examples: durian,chillies,mango and papaya.
  • Growth curve:-
Annual plant

Source:[Text Book Biology KSSM Form 5]
Biennial plants
Source:[Text Book Biology KSSM Form 5]
Perennials plants
Source:[Text Book Biology KSSM Form 5]