The Leaf

​ The Leaf

By Pavitra BP

Open Ended

What are the two main parts of a plant?

• The part of the plant that grows under the ground

• Grows downwards-away from sunlight

• Brown , non-green part of the plant

• Arises from the base of the stem.

• End part of root branches has hair like structures called root hair

​

​Root System

• ​Made up of primary- main thick root and secondary roots-many side branches.

• Eg- Gram and Pea plant

​​Tap Root System

• ​Has many roots of around the same size and thickness.

• They arise from the base of the stem forming a cluster. Eg. Grass, Maize

​​ Fibrous Root System

​​Types of Root System

​Functions of Roots

• Fixation - Roots hold the plant firmly to the soil. They bind particles of the soil.

• Absorption - They absorb water and minerals from the soil.

• Grows above the ground- main part-stem

• Grow upwards and hold the plant.

• Node- part of the stem where the leaf grows.

• Internode- region between 2 adjacent nodes

• Buds- undeveloped shoots

• Terminal/ Apical bud- present at the tip of the stem

• Axillary bud- found in the axil

( Axil - the upper angle between the leaf
and the stem)

​

​ The Shoot System

Functions of Stem

1. Support - Bears branches, buds, leaves, flowers and fruits.

2. Conduction - Conducts water and minerals from roots to other parts.

It also conducts the prepared food from the leaves to the other parts of
the plant.
3. Food Production- Some green stems contain chlorophyll. The manufacture
food.
4. Orientation of leaves - On the stem, the leaves are arranged in a way that
they get maximum sunlight.

1. Petiole - the stalk that attaches the leaf to the stem. ( In some leaves, the stalk is absent and they are directly attached to the stem- sessile leaves)

2. Lamina/Leaf Blade- Flat, broad, green part.

3. Midrib- Petiole continues into the lamina at the centre as the thick midrib. It gives rise to fine branches called veins. They give support to the leaf and conduct water, minerals and food.

   
   
   
   

​

​ Parts of a Leaf

• A leaf with a single lamina.

• Axillary bud is present.

• Eg. Mango, peepal, banyan

​​ Simple Leaf

• ​A leaf in which the lamina is divided into leaflets.

• Leaflets do not have axillary bud in their individual axis.

• Eg. Rose, Neem, Gulmohar

​​ Compound leaf

​​Types of Leaves

​Different Shapes Of leaves

​Heart Shaped-
Peepal

​Oval Shaped- Apple

​Needle shaped- Pine

​Sword Shaped- Neerium

​Oblong shaped- Banana

​Circular- Lotus

​Tapered- Eucalyptus

​Linear-Grass

​ Different Types Of Edges of Leaves

​Entire/Smooth- Mango

​Serrate/ Toothed (pointed forward) - Rose

​Crenate- Bryophyllum

​Lobed leaf

​Different textures of leaves

​1. Smooth and soft
2. Rough and Hairy
3. Fleshy and thick
4. Thin and papery
5. Juicy
6. Dry

​ Arrangement of Leaves

​The leaves are arranged on a stem in different ways to get maximum exposure to air and sunlight.
Phyllotaxy- The arrangement of leaves on a stem or branch is called phyllotaxy.
Three main types of arrangements are

​1. Alternate

​2. Opposite

​3. Whorled

Veins form a net-like pattern on both sides of the midrib.
Eg- Peepal, Mango, Mustard

1. Reticulate Venation

Veins run parallel to each other or parallel to the midrib.
Eg . Banana, Wheat, Grass

​​ 2. Parallel Venation

​​Venation- The arrangement of veins on a lamina

Functions of the Leaf

1. Manufacture of Food (Photosynthesis)

• It is the main function of the leaf.

2. Transpiration

• It is the loss of water in the form of water vapour mainly from the surface of the leaves.

• It helps the roots absorb more water along with minerals.

• It also has a cooling effect on plants.

3. Exchange of Gases
   

• The exchange of gases- carbon di oxide and oxygen takes place mainly through the surface of leaves

​Photosynthesis

• ​Green plants make their own food, so they are called autotrophs. (troph means feeding/nourishment).

• This type of nutrition is called autotrophic nutrition.

• Plants make their own food by the process of photosynthesis.

• The process by which green plants make their own food (glucose) from carbondioxide and water in the presence of sunlight and chlorophyll is called photosynthesis.

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​Section of a Leaf

​Stomata

​Structure of Stomata

​2 videos from folder

​ End Products of Photosynthesis

​The 2 end products of photosynthesis are 1. Glucose and 2. Oxygen
1. Glucose
It is a simple sugar.
It is utilized by the plants immediately.
The extra glucose is converted into starch and sucrose. These are either stored or utilised for the synthesis of proteins and fats.

2. Oxygen
It is used for respiration by the plants.
A major part of the oxygen produced is released in the atmosphere through stomata.
This oxygen is utilized by all other living organisms for respiration.

​Factors affecting photosynthesis

1. Light

2. Availability of carbon di oxide and water

3. Temperature (20 - 35 degree celcius)

​Importance of Photosynthesis

Transpiration

​Factors affecting Transpiration

1. Sunlight
2. Temperature
3. Wind
4. Humidity

​The loss of excess water from plants mainly through leaves as water vapour is called transpiration.

​Importance of Transpiration
Maintains concentration of sap and has cooling effect

Modification of Leaves

​Sometimes a leaf, or a part of it is modified to perform a specific function. These kinds of leaves are called modified leaves.

Regular Plants
1. Tendrils
2. Spines
3. Scaly Leaves

Insectivorous Plants
1. Pitcher Plants
2. Bladderwort
3. Venus flytrap (Videos from folder)