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Biology Project

Jyoti Sharma

on 10 January 2014

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Transcript of Leaves

Leaves are the power house of plants
A leaf has many layers, the first outer surface which is a thin waxy covering is called cuticle, the function of this layer is, to prevent water loss. Directly underneath the cuticle is a layer of cells called the
Within the leaf, there is a layer of cells called mesophyll. Mesophyll can be divided into two layers, the
and the
The Palisade cells are more column-like, and lie under the epidermis, the spongy cells are more loosely packed and lie between the palisade layer and the lower epidermis.
Leaf Adaptation to Abiotic Factors
The air spaces between the spongy cells allow for gas exchange. Mesophyll cells (both palisade and spongy) are packed with chloroplasts, and this is where photosynthesis actually occurs.
Mesophyll cont.
Functions of the Leaves
Leaves are the major site of food production for the plants
The process plants use to produce food for itself is called
is the process of converting light energy, usually from the sun to chemical energy and storing it in the bonds of sugar
Photosynthesis takes place in the leaves because they contain chlorophyll found in the chloroplasts
are the green pigment necessary to capture light energy
The building blocks for sugar and starch are the obtained carbon dioxide and water
Equation for photosynthesis:
Carbon dioxide + water + light energy glucose + oxygen + water
Plants cannot survive in extreme conditions in some
terrestrial environments

Conifers are mostly evergreens and keep their leaves throughout the season

Their leaves are modified (long, thin needles), with a small surface area and a thick waxy cuticle

The leaves are inefficient for photosynthesis but they reduce water loss, especially in the winter
Abiotic Factors Cont.
Leaves with a thick layer of water storage tissue prevent water loss

Plants with those characteristics can survive in areas of high salt content or low precipitation in their soil

These plants have less than the usually number of stomata and reduce water loss

Photosynthesis takes place in fleshy, green stem
Interchange of Gases
Leaf Adaptation to Biotic Factors
Leaves are vulnerable to herbivores and they prefer leaves that are tender and have mild flavors

Leaves that are tough, hairy, prickly, or bitter are more likely to survive from being a herbivores’ appetite

The trade-off between herbivores and leaves is, the very characteristic that helps plants survive, herbivores reduce their photosynthetic efficiency
Biotic Factors

Diversity helps herbivores cope with different plant features

Diversity of plants can either continue to supply nutritious food for herbivores or produce toxic chemicals in their tissues which control herbivore populations
Other Leaf Adaptations
During photosynthesis, the leaf must acquire a constant supply of carbon dioxide and be able to release the oxygen produced
The exchange of gas occur through tiny pores called the
(singular: stoma)
Stomata cont.
As well as regulating carbon dioxide and oxygen diffusion, stomata also allows water vapour to escape from the leaf
The loss of water vapour is called
The water diffuses and evaporates into the air spaces of the leaves, and out to the atmosphere through the stomata
The functions of the epidermis in the leaf are; to protect against water loss, regulate gas exchange, secrete metabolic compounds and absorb water and mineral nutrients.
Guard Cells
Plants rely on their vascular system to deliver water and nutrients to their cells.

The plants vascular system is comprised of two main types of vascular tissue:
– Xylem conducts water and dissolved minerals absorbed from the soil through the plant.
– The phloem conducts nutrients, which are made in the leaves, to all the cells in the plant.

The opening and closing of each stoma is regulated by a pair of Guard cells
Guard cells contain chloroplasts and are around each stoma in the epidermis of a leaf or a stem
When the stomata are open, the plant can obtain needed carbon dioxide, but at the same time, the plant loses water
When the stomata are closed, water is conserved, but the carbon dioxide can't be obtained
http:// www.fairchildgarden.org/uploads/docs/Education/Downloadable_teaching_modules/green%20machines/Anatomy%20and%20Physiology%20of%20Leaves.pdf
Textbook pages: 501- 507
Some leaves are modified and others have regular leaves within modified ones

Specialized leaves survive better than leaves that are not, especially when dealing with herbivores

There are a variety of plants that have lost their ability to photosynthesize and also lost their leaves

These plants are considered heterotrophic, and get their nutrients from decaying organic material in the soil
Indian Pipe
Photosynthesis cont.
When there is plenty of water in the guard cells, they increase in size and open the stomata.
When the water content decreases, the guard cells collapse, which closes the stomata.
Types of leaves
There are two different types of leaves: simple and compound.
A simple leaf may have incisions but these incisions are not deep enough to divide the blade into leaflets.
The blades of compound leaves are divided into distinct parts, called leaflets.
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