Plants: Leaves

Leaves• Play role in photosynthesis, gas exchange, storage, and

protection from predators.• Leaf cells absorb energy from sunlight in a chloroplast which

contains photopigments.• Photopigments are chemicals that absorb particular

wavelengths of red and blue light and reflect green light.

Leaf Structure

• Make sugar and supplies all living organisms with food and oxygen

• Designed so they can capture the most amount of sunlight.

• Covered with a waxy cuticle that is produced by the epidermis. Both provide protection.

• Stomata are little passages on the underside of leaves that allow for gas and water vapour exchange. Woody plants have no stomata on the upperside, herbaceous plants do have stomata on the upperside.

• Stomata are open during the day and closed at night

• Carbon dioxide is used by chloroplasts to perform photosynthesis

• Carbon dioxide is brought into the plant through the stoma, while oxygen and water are released into the atmosphere.

• Photosynthesis cannot happen at night, so the stomata are closed.

• Each stoma is surrounded by two guard cells that are kidney-shaped, specialized epidermal cells with chloroplasts• Water moves into the guard cells during the day

because of all the ions that move into the cells.• The inside is thicker, so the outside can expand

more, creating a hole between the two cells.

• Cells within the leaf are the mesophyll cells that have a lot of chloroplasts and have two layers:

• Palisade layer that are densely packed and have more chloroplasts

• Spongy layer that are loosely spaced so air can come in contact with the cells.

• Water loss from the leaves through evaporation is called transpiration

• The xylem and phloem continue from the stems into the leaves in special vascular bundles called veins.

• Monocot veins run parallel to each other

• Dicot veins run in a branching network

Leaf Specializations

• Dry climate: thicker cuticle, stomata on underside.

• Cactus leaves are modified into spines

• Aquatic plants have stomata on the upperside for gas exchange.

• Onion bulb: stores water and carbs

Leaf Uses

• Provide important nutrients and food energy in the diets of humans.

• Use them for herbs and spices

• Teas

• They are nutritious (calcium, potassium, iron, magnesium, vitamins B, C, E, K)

• Use waxy cuticle for polishes, cosmetics, candies.

Leaves and Chemicals

• Leaves produce chemicals that humans have used in the past and present as medicinal.

• Research one medicinal plant and report on what it is used for as homework tonight