The Leaf

The leaf, connected by its petiole and expanding into the lamina with its network of veins, is far more than just a pretty sight. It’s the plant’s powerhouse for photosynthesis, using sunlight and chlorophyll to convert carbon dioxide and water into glucose and oxygen. Through tiny pores called stomata, mainly on the lower surface, leaves also manage water balance and temperature via transpiration. Like us, they respire, taking in oxygen.

Beneath the protective epidermis, often dotted with stomata, lies the mesophyll, rich in chlorophyll for sugar production. Veins act as transport networks, delivering water and nutrients and carrying away sugars.

Leaves exhibit incredible diversity, from simple, single blades to compound leaves with multiple leaflets, and varying vein patterns. Specialized leaves showcase remarkable adaptations: cactus spines for defense, vine tendrils for climbing, and succulent leaves for water storage. Truly, these green wonders are essential and remarkably adaptable, fulfilling numerous vital roles in a plant’s life.

Review Questions

1. Tick (✓) the appropriate answer:

(i) Identify the plant which has compound leaves:
(a) Banana
(b) Banyan
(c) Mango
(d) Rose

Ans : Rose

(ii) Which one of the following is not an insectivorous plant—
(a) Pitcher plant
(b) Venus flytrap
(c) Bladderwort
(d) Cactus

Ans : Cactus

(iii) This leaf shows parallel venation:
(a) Banana
(b) Mango
(c) Banyan
(d) Guava

Ans : Banana

(iv) The point on the stem from where the leaf arises is:
(a) Petiole
(b) Lamina
(c) Node
(d) Trunk

Ans : Node

(v) Which one of the following is essential for photosynthesis:
(a) Carbon dioxide
(b) Nitrogen
(c) Oxygen
(d) Soil

Ans : Carbon dioxide

Question 2.
Name the following:
1. The part of the plant which grows under the ground 

Ans : Root

2. The part of the plant which grows above the soil

Ans :  Shoot

Question 3.
Differentiate between the following:
(i) Tap root and Fibrous root
Ans :

Feature	Tap Root System	Fibrous Root System
Structure	Has one main, thick primary root that grows vertically downwards. Smaller lateral roots (secondary and tertiary roots) branch off from the primary root.	Consists of a dense network of thin, similarly sized roots that spread out from the base of the stem. No single dominant root.
Origin	Develops from the radicle (embryonic root) of the seed.	Develops from the base of the stem or sometimes from leaves (adventitious roots). The primary root (from the radicle) is usually short-lived and replaced.
Depth in Soil	Typically grows deep into the soil.	Generally remains closer to the soil surface (shallow).
Number of Roots	Usually has one prominent main root.	Has a large number of thin, branching roots.
Thickness of Roots	The primary root is thick and tapers downwards.	Roots are generally thin and of similar thickness.
Anchorage	Provides strong and firm anchorage, especially for taller plants.	Provides less strong anchorage compared to tap roots, but the dense network helps in holding the topsoil.
Absorption	Can absorb water and minerals from deeper soil layers.	Efficient at absorbing water and nutrients from the upper layers of the soil due to the extensive network.
Food Storage	The main root can be modified for food storage (e.g., carrot, radish, turnip).	Roots are generally not modified for significant food storage.
Soil Erosion	Less effective at preventing topsoil erosion.	The dense network of roots is effective in binding the soil and preventing erosion.
Plant Type	Commonly found in dicotyledonous plants (dicots).	Commonly found in monocotyledonous plants (monocots) and ferns.
Leaf Venation	Plants usually have leaves with reticulate (net-like) venation.	Plants usually have leaves with parallel venation.
Examples	Carrot, radish, beetroot, mustard, mango, oak.	Grasses, wheat, rice, banana, coconut palm, onion.

(ii) Simple Leaf and compound leaf

Ans : 

Feature	Simple Leaf	Compound Leaf
Leaf Blade	Consists of a single, undivided leaf blade (lamina). The blade may be lobed or have teeth, but it is still one continuous piece.	The leaf blade is divided into two or more separate smaller units called leaflets.
Attachment	Attached to the stem by a single petiole.	Leaflets are attached to a common point or along a central axis (rachis) which is attached to the stem by a single petiole.
Bud at Axil	An axillary bud (which can develop into a branch or flower) is present at the axil of the petiole (the angle between the petiole and the stem).	Axillary buds are present at the axil of the entire compound leaf’s petiole, but not at the axil of individual leaflets.
Appearance	Looks like a single, complete leaf.	Appears to be composed of several smaller leaves attached to a central stalk.
Detachment	The entire leaf falls off at the abscission layer at the base of the petiole.	The leaflets may fall off individually, or the entire compound leaf (with the rachis and leaflets) falls off at the abscission layer at the base of the petiole.
Examples	Mango, guava, hibiscus, maple, oak, banana.	Neem, rose, tamarind, clover, silk cotton, ferns.

(iii) Parallel venation and reticulate venation

Ans :

Feature	Parallel Venation	Reticulate Venation
Vein Arrangement	Veins run parallel to each other from the base to the tip of the leaf. They may be connected by small, straight veinlets running perpendicular to the main veins.	Veins are arranged in a net-like or web-like pattern throughout the leaf blade. There is usually a prominent midrib from which smaller veins branch out irregularly, further dividing into veinlets.
Appearance	The veins appear as straight lines running alongside each other.	The veins form a network or mesh-like structure.
Midrib	May have a prominent midrib running along the length, with other veins parallel to it, or several main veins running parallel from the base.	Typically has a prominent central midrib from which other veins branch out.
Veinlets	Small veinlets, if present, run perpendicular to the main veins.	Veinlets form a dense, irregular network connecting the larger veins.
Association with Root System	Typically found in plants with a fibrous root system.	Typically found in plants with a tap root system.
Association with Leaf Type	Commonly found in simple leaves that are often long and narrow.	Commonly found in both simple and compound leaves that are often broad.
Plant Group	Characteristic of monocotyledonous plants (monocots) like grasses, banana, maize, wheat, lilies, and palms.	Characteristic of dicotyledonous plants (dicots) like mango, rose, hibiscus, beans, and oak.
Examples	Banana leaf, grass leaves, maize leaves, palm leaves.	Mango leaf, rose leaf, hibiscus leaf, bean leaf, oak leaf.

Question 4.

What are the four functions of the roots ?

Answer :

Holding Firmly: Roots act like anchors, gripping the soil tightly to keep the plant upright and stable, preventing it from toppling over due to wind or rain.

Drinking Water: They soak up water from the soil, like tiny straws drawing in the moisture that the plant needs to survive and grow.

Eating Nutrients: Roots also absorb essential nutrients and minerals from the soil, which are vital for the plant’s healthy development and overall well-being, just like how we need vitamins and minerals.

Storing Goodies: In some plants, roots act as storage units, holding extra food (like starches) that the plant can use later for energy or to grow new parts. Think of carrots or radishes!

Question 5.

Mention the functions of the following :

(i) Spines

(ii) Tendril

(iii) Scale leaves

Answer :

(i) Spines: That’s where spines come in handy! These are essentially modified leaves that have become sharp and pointed. Their main job is defense, acting like tiny, natural needles to deter herbivores from taking a bite. Think of a cactus in the desert – those sharp spines aren’t just for show; they help the plant survive by discouraging thirsty animals from munching on its water-storing tissues.

(ii) Tendrils: Now picture a plant that needs support to climb towards the sunlight. Tendrils are the plant’s natural climbing tools! These are often modified leaves or stems that are thin, wiry, and very sensitive to touch. When a tendril encounters a support like a fence, a twig, or even another plant, it will coil around it, helping the plant to climb upwards. Think of a pea plant reaching for the sky – those delicate, curling tendrils are what allow it to vine and climb. Their primary function is support.

(iii) Scale leaves: Scale leaves are a bit different; they’re not designed for the typical leaf job of photosynthesis. Instead, they are usually small, often dry or papery, and their main functions are protection and sometimes storage. You might find them covering buds to shield the delicate developing leaves inside from harsh weather or physical damage. In some plants, scale leaves can also store food or water. Think of the brown, papery coverings on a developing bud – those are scale leaves doing their protective work.

6. Define venation. What are the different types of ve-nation found in the leaves

Ans:

Venation is defined as the arrangement or pattern of veins and veinlets in the lamina (leaf blade) of a leaf. The veins contain vascular tissues (xylem and phloem) that help in the transport of water, minerals, and food throughout the leaf. Venation also provides structural support to the leaf blade.

There are primarily two main types of venation found in leaves:

1. Reticulate Venation:
   • In this type of venation, the veins are arranged in a net-like or web-like pattern throughout the leaf blade.
   • There is usually a prominent midrib (the central vein) from which smaller veins branch out irregularly, and these further subdivide into veinlets, forming a complex network.
   • Reticulate venation is characteristic of dicotyledonous plants (dicots).
   • Examples: Mango, rose, hibiscus, bean, oak, guava.
2. Parallel Venation:
   • In this type of venation, the veins run parallel to each other from the base to the tip of the leaf.
   • They may be connected by small, straight veinlets that run perpendicular to the main veins.
   • A prominent midrib may or may not be present; if present, the other veins run parallel to it. In some cases, there are several main veins running parallel from the base.
   • Parallel venation is characteristic of monocotyledonous plants (monocots).
   • Examples: Grasses, wheat, rice, banana, maize, palm.

Question 7.

Describe the modifications of leaves in any one insec-tivorous plant.

Answer :Isn’t it fascinating how the pitcher plant has these leaves that have completely changed into these pitcher-shaped traps? The middle part of the leaf stretches out like a little rope to help it climb, and the actual leaf turns into this vibrant, nectar-filled pitcher. It even has this tricky rim that makes it hard for bugs to get out. And get this – inside, there are these juices that dissolve the insects, giving the plant the nutrients it really needs, especially since it lives in places where the soil isn’t very rich. It’s such a clever way for the plant to survive!

Question 8.

Write the two main functions of leaves.

Answer  :Making Food (Photosynthesis): Leaves are like tiny food factories for the plant. This process, called photosynthesis, is how plants get the energy they need to live.
Breathing and Losing Water (Gas Exchange and Transpiration): Leaves also have tiny holes that allow them to take in air (including carbon dioxide needed for making food and oxygen for breathing) and release waste gases. They also let out water vapor through these holes in a process called transpiration, which helps move water up from the roots.

Question 9.

What is the modification seen in the Bryophyllum? Explain.

Answer :Bryophyllum’s leaves have this neat trick! The edges grow tiny baby plants that just drop off and become new Bryophyllum. ¹ Pretty cool way to make more of themselves without any seeds involved

Question 10.

Define:

(i) Photosynthesis

(ii) Transpiration

Answer :(i) Photosynthesis: This is how green plants use sunlight, water, and carbon dioxide to create their own food (sugars) and release oxygen as a byproduct. 

(ii) Transpiration: This is essentially the process where plants lose water vapor through tiny pores, mostly on their leaves. It’s like the plant “sweating” and helps to pull water up from the roots.

Question 11.

Name the wide flat portion of the leaf

Answer :Lamina

Question 12.

What purpose is served by the spines horned on the leaves of cactus.

Answer :Defense: They act as a physical barrier, deterring herbivores from feeding on the plant’s fleshy stems, which store water.  

Water Conservation: By creating shade and trapping a layer of air close to the plant’s surface, the spines help reduce water loss through transpiration, a vital adaptation in arid environments

Question 13.

Explain why leaf survival is so important to the plant?

Answer :Photosynthesis: Leaves are the main sites where photosynthesis occurs. This is the amazing process where plants use sunlight, water, and carbon dioxide to create their own sugars (glucose) for energy and growth, releasing oxygen as a byproduct. Without healthy, functioning leaves, the plant can’t produce the energy it needs to survive, grow, reproduce, and defend itself against diseases and pests.  

Energy Reserves: The sugars produced during photosynthesis are either used immediately or stored as starch for later use. When leaves are damaged or lost, the plant’s ability to build up these crucial energy reserves is severely hampered. This can weaken the plant over time, making it less resilient to environmental stresses.  

Water Regulation (Transpiration): Leaves play a key role in transpiration, the process by which water evaporates from the leaf surface. This evaporation creates a pulling force that helps draw water and essential nutrients up from the roots to the rest of the plant. Healthy leaves ensure this vital transport system functions efficiently.

Nutrient Acquisition: While roots primarily absorb nutrients from the soil, leaves can also absorb certain nutrients directly from the atmosphere or through foliar feeding (when humans apply nutrient solutions to leaves). Loss of leaves reduces the plant’s overall capacity for nutrient uptake.

Gas Exchange (Respiration): Just like animals, plants need to respire, taking in oxygen and releasing carbon dioxide to fuel their metabolic processes. Leaves have tiny pores called stomata that facilitate this gas exchange. Healthy leaves ensure proper respiration.

Question 14.

Give an example of the following and draw generalized diagrams for the same:

(i) Simple leaf and compound leaf.

(ii) Parallel venation and reticulate venation.

Answer : 

(i) Simple leaf and compound leaf.

Ans : Simple Leaf:

• A leaf with a single, undivided blade.
  
• Even if lobed, the lobes do not touch the midrib deeply enough to make separate leaflets.
  
• Example: Mango (Mangifera indica), Guava (Psidium guajava).

Compound Leaf:

• A leaf in which the blade is divided into distinct leaflets.
  
• Each leaflet may appear like a leaf but lacks a bud at its base.
  
• Example: Neem (Azadirachta indica), Rose (Rosa).

(ii) Parallel venation and reticulate venation.

Ans : 

Parallel Venation

• Definition: Veins run parallel to each other.
  
• Example: Banana leaf (Monocot)

Reticulate Venation

• Definition: Veins form a net-like pattern.
  
• Example: Peepal leaf (Dicot)
  

Question 15.

In list some of the advantages of transpiration to green plants.

Ans : 

Absorption and Transport of Water and Minerals: Transpiration creates a pulling force (transpiration pull) that helps in drawing water and dissolved minerals from the roots up through the xylem to the rest of the plant, including the leaves. This upward movement is essential for various metabolic activities.

Cooling Effect: The evaporation of water from the leaf surface during transpiration has a cooling effect on the plant, similar to how sweating cools animals. This is particularly important in hot weather to prevent the plant from overheating and its enzymes from denaturing.

Distribution of Water: Transpiration ensures a continuous supply of water to all parts of the plant, which is crucial for photosynthesis, cell turgidity (keeping cells firm and the plant upright), and overall growth.

Maintenance of Turgor Pressure: The loss of water through transpiration and its subsequent uptake helps maintain turgor pressure within the plant cells. 

Removal of Excess Water: While transpiration is a necessary process, it also helps in removing excess water that the plant might have absorbed from the soil.

Photosynthesis: By facilitating the transport of water to the leaves, transpiration indirectly supports photosynthesis, as water is one of the essential raw materials for this process.

Question 16.

Why do some plants have to trap insects ?

Ans :

Some plants trap insects because they live in nutrient-poor environments, especially soils lacking enough nitrogen. ¹ By digesting insects, they obtain the essential nutrients they can’t get from the soil. ² It’s their way of supplementing their diet!

Question 17.

Explain some of the modifications of leaves found in plants.

Answer :

Leaves are pretty adaptable and have evolved some cool modifications to perform different jobs. Here are a few:  

• Tendrils: In plants like peas and vines, leaves can transform into slender, wiry structures called tendrils. These help the plant climb and support itself by twining around objects.  
• Spines: Think of cacti! Their sharp spines are actually modified leaves. These protect the plant from herbivores and also reduce water loss by minimizing the surface area exposed to the sun and wind.  
• Storage Leaves: Some plants, like onions and succulents (like aloe vera), have fleshy leaves that are adapted for storing water and nutrients.  
• Reproductive Leaves: In plants like Bryophyllum (also known as mother of thousands), leaves can develop buds along their margins that can grow into new, independent plantlets.  
• Insect-trapping Leaves: Carnivorous plants like the Venus flytrap and pitcher plants have highly specialized leaves designed to trap and digest insects for nutrients

Question 18.

What is a tendril ? Explain its use to the plant.

A tendril is a slender, thread-like appendage of a climbing plant, often a modified leaf, that stretches out and twines around any suitable support. As mentioned earlier, plants like peas and vines use tendrils to climb and support themselves. The image you provided shows tendrils on a sweet pea plant.

Question 19.

Complete the crossword using the clues given below. Check your performance with the correct solutions given at the end of the chapter.

Answer :

Clues Across:

1. Plant that bears buds in leaves for propagation. – BRYOPHYLLUM
2. The flattened green part of the leaf. – BLADE
3. Underground plant part. – ROOT
4. Structure that develops into flowers. – BUD

Clues Down:

5. The central big vein of a leaf. – MIDRIB
6. A modification seen in cactus. – SPINE