Leaf Botany and Plant Cell Biology Part 1

University:
Sam Houston State University
Course:
BIOL 5350 | Plant Evolutionary Biology
Academic year:

2022
Views:

215

Pages:

10
Author:

5CelestialChronicle

Leaf Botany and Plant Cell Biology Leaf Function • The main function of leaves is to absorb sunlight and use this energy to produce sugars ▫ This is the process of photosynthesis ▫ Photosynthesis is the creation of sugar from carbon dioxide and water using the energy of the sun • Leaves are usually flat so that they can absorb the maximum amount of light as efficiently as possible. Leaf Anatomy • A leaf is connected to the stem by a structure called the petiole. ▫ The base of the stem where the petiole connects is called the node ▫ Where the petiole connects to the leaf is called the axil ▫ The axil is where we happen to find buds, clusters, and emerging leaves. Cross section of a leaf • A leaf blade consists of several layers • The outer layer (top and bottom) is the epidermis ▫ Its main function is protection of the leaf Epidermis • The epidermis layer can be specialized • For example, some leaves have hairs for protection. • The cuticle is a part of the epidermis that produces cutin ▫ Cutin is a waxy layer that protects the plant from dehydration and disease. ▫ Increasing light intensity will increase the thickness of the cutin layer ▫ Hence the need for hardening off before moving plants Cutin • Cutin also repels water • This can make some pesticides less effective unless they have additives to help them penetrate the cutin layer ▫ Without these additives, the insecticide would completely flow off of the plant Guard Cells • Specialized epidermal cells called guard cells are like valves to a leaf ▫ They can open and close in response to weather, light, and moisture ▫ They regulate the passage of water, oxygen, and carbon dioxide • The openings in guard cells are called stomata. ▫ Most stomata are found on the underside of leaves • Conditions that would cause a plant to lose water (high temp, low humidity) cause the guard cells to close, sealing off the stomata. ▫ Guard cells also close in absence of light Mesophyll • The mesophyll layer is found in the middle of the leaf • The mesophyll has two layers ▫ The dense upper layer is called the palisade layer ▫ The air-filled soft lower layer is called the spongy mesophyll • The mesophyll is important because this is where photosynthesis takes place Review • Outer Layer – Epidermis consisting of… ▫ Cuticle ▫ Guard Cells ▫ Stomata • Inner Layer – Mesophyll, consisting of… ▫ Palisade Layer ▫ Spongy Mesophyll • Epidermis = Protection • Mesophyll = Production Types of modified leaves • Scale leaves (cataphylls) are found on rhizomes and buds, which they enclose and protect. • Seed leaves (cotyledons) are found on embryonic plants. They store food for the developing seedling. • Spines and tendrils, such as those found on barberry and pea plants, protect a plant or help support its stems. • Storage leaves, such as those on bulbous plants and succulents, store food. • Bracts often are brightly colored. For example, the showy structures on dogwoods and poinsettias are bracts, not petals.

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