Photosynthesis (leaf structure)

Leaf Structures• To understand photosynthesis it is

important to understand the leaf structures and functions.

• Leaves are the plants “food supply factory.”– In higher plants the leaf structures is adapted

to maximize light absorption and carbon dioxide diffusion.

Leaf structures• Veins (xylem and phloem)• Mesophyll• Palisade layer (parenchyma cells)• Spongy Layer• Cuticle• Upper and Lower epidermis• Stomates• Guard cells

Veins (xylem and phloem)• This is a network that acts like a plumbing system

that supplies water and minerals to the leaf and that carries the products of photosynthesis away to other parts of the plant.

• Xylem: carries water and dissolved minerals from the roots to the leaves

• Phloem: carries the food made in the leaves to the rest of the plant

Mesophyll• The green leaf cells between the upper and

lower epidermis of a leaf which is loaded with chloroplasts.

• The mesophyll consists of 2 layers:–Palisade layer (parenchyma cells)– Spongy Layer

Palisade layer (parenchyma cells)• This layer is found right below the upper

epidermis, which is made of parenchyma cells.• Most photosynthesis in plants takes place in

the palisade layer of the leaves

Spongy Layer• This layer is found below the palisade layer and

above the lower epidermis, which contains many air spaces.

• The spongy layer is involved in gas exchange.

Cuticle• This is a thin non-living waxy substance that

covers leaves.• The cuticle helps reduce water loss and

protection from most bacteria, fungi, and insects.

Upper and Lower epidermis• This is a single layer of cells, which covers the

upper and lower surfaces of leaves.• The epidermis also provides protection to the

leaves from most bacteria, fungi, and insects.

Stomates• Are minute pores found in the epidermis of leaves,

which allows diffusion of gases in and out.• During the day, stomata absorb carbon dioxide

from the air and release oxygen and water.• Evaporation of water from the leaf is referred to as

transpiration, is the major source of water loss in leaves.

Guard cells• Are two bean-shaped cells that surround the

stomata.• The guard cells control the size of the stomata.• When the guard cells swell, the stomata open.• When the guard cells shrink, the stomata close.

ChloroplastChloroplast- a organelle in plant cells and algae that contain the chlorophyll pigments and the enzyme systems for photosynthesis.

Chloroplast

Chlorophyll a light absorbing pigment that gives plants their green color and converts the energy of sunlight to food in the process known as photosynthesis.

Plant leaf pigments