Long Answers

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Last edited 25 days ago by Learn LoopHQ.

Chapter: 01. The Leaf

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Name the main parts of a typical leaf and describe their functions.

A typical leaf consists of the petiole and the lamina. The petiole is the stalk that attaches the leaf blade to the stem, sometimes having a swollen leaf base. The lamina, or leaf blade, is the green, flat, and expanded part where most food production occurs. Supporting the lamina is the midrib, which forms its central axis. From the midrib, veins branch out, and these further divide into veinlets, forming a network that provides support to the lamina, distributes water and minerals, and transports manufactured food throughout the plant.

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Explain the two primary types of venation found in leaves, providing examples for each.

The arrangement of veins in a leaf is called venation, primarily categorized into two types: reticulate and parallel. In reticulate venation, the veins and veinlets form an intricate net-like pattern throughout the lamina, resembling a web. This type is characteristic of dicot plants, with examples including the leaves of Peepal, Mango, and Guava. Conversely, parallel venation is where the veins run parallel to each other, typically extending from the base to the apex of the leaf without forming a network. This pattern is characteristic of monocot plants, seen in leaves like those of Banana, Maize, and Wheat.

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Describe the processes of photosynthesis and transpiration, highlighting their importance to a plant.

Photosynthesis is the vital process where green leaves manufacture food for the plant using sunlight, carbon dioxide from the air, and water absorbed by roots. Chlorophyll, the green pigment, captures solar energy, converting it into chemical energy stored in glucose (which becomes starch). This process also releases oxygen. Transpiration is the loss of excess water from the leaf surface as water vapor through tiny pores called stomata. Both are crucial: photosynthesis provides the plant with essential food for growth and survival, while transpiration cools the plant and creates a suction force that helps in the absorption and transport of water and minerals from the soil.

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Elaborate on how leaves are modified for support and protection, providing examples for each.

Leaves exhibit various modifications to perform specialized functions like support and protection. For support, some leaves develop into thin, coiled structures called leaf tendrils, as seen in sweet pea and garden pea plants; these tendrils wrap around other objects, enabling the plant to climb. For protection, leaves can be modified into sharp spines, like in cacti, which deter grazing animals and significantly reduce water loss through transpiration. Another protective modification includes scale leaves, found in plants such as ginger and onion, which are often thin and dry or thick and fleshy, primarily serving to protect developing buds and sometimes storing food.

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Explain why insectivorous plants consume insects and describe two examples of such plants.

Insectivorous plants, although green and capable of photosynthesis for carbohydrates, consume insects primarily to supplement their nitrogen intake. They typically grow in nitrogen-deficient environments, such as swampy or boggy soils, where essential nitrogen compounds are scarce. Two examples include the Pitcher plant and the Venus flytrap. The Pitcher plant has its lamina modified into a pitcher with a lid; insects are attracted, fall in, and are digested by secreted juices. The Venus flytrap has a lamina divided into two hinged lobes with sensitive trigger hairs; when an insect touches these hairs, the lobes snap shut, trapping and then digesting the prey.

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How do leaves contribute to vegetative propagation in certain plants? Explain with an example.

Leaves play a significant role in vegetative propagation, a form of asexual reproduction, in specific plants. Instead of relying on seeds, these plants can grow new individuals directly from their leaf structures. This occurs when specialized adventitious buds develop along the margins of the leaves. If these leaf buds come into contact with moist soil, they are capable of developing roots and then growing into complete, independent plantlets. A classic example of a plant that uses its leaves for vegetative propagation is Bryophyllum, where new plantlets can be seen emerging directly from the notches on the edges of its leaves.

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