Photosynthesis- Leaf Structure and How it Relates to Photosynthesis Flashcards
Draw, label and annotate the external view of a dicot leaf.
vein
margin
blade
Why are leaves thin?
The leaves of a plant must be thin so that gases will have a short distance to diffuse to different parts of the leaf and light will be easily absorbed by the photosynthetic cells in the leaf.
What does the stomata aid in?
the stomata that are found on both the upper and lower surface of the leaves. they are also responsible for the accessibility of carbon dioxide.
What does the xylem in the veins of the leaves provide?
Water
Why must leaves contain chlorophyll and other pigments?
To absorb light energy?
Why must leaves have a large surface area?
For the absorption of light and diffusion of gases.
Draw, label and annotate the t.s. of a dicot leaf.
Upper Epidermis- consists of a single layer of cells which are thin, flat and transparent to allow light to pass through to the palisade mesophyll below. A waxy cuticle may be present to reduce the loss of water. There may be guard cells and stomata present.
Palisade Mesophyll- this consists of one or more layers of long almost cylindrical cells arranged at right angles to the upper epidermal cells. This is so as to reduce the number of light absorbing cross-walls in the upper part of the leaf so that maximum light can reach the chloroplasts. The palisade mesophyll contains cells with the largest number of chloroplasts. The cells have large vacuoles which store water to be used by chloroplasts during light dependent reactions. The cells have thin peripheral cytoplasm so the chloroplasts are located just below the cell wall where light can reach them easily. The chloroplasts can be moved around in the cytoplasm by microtubules. At low light intensities they can be moved to the upper part of the cells and at higher light intensities they can be moved further away from the upper part of the cell to avoid being damaged by excess light. There are long narrow air spaces between the cells to ensure that carbon dioxide gas can reach the cells for photosynthesis. The cells have thin walls so that gases can diffuse easily into and out of the cells and light can pass through easily into the cytoplasm where the chloroplasts are located.
Spongy Mesophyll- The cells in this layer are arranged loosely and in an irregular arrangement with large air spaces between them. This arrangement increases the internal surface area for gaseous exchange since these cells contain chloroplasts and carry out photosynthesis. Veins are found in this region of the leaf and contain xylem and phloem.
Lower Epidermis- this is a thin, flat layer consisting of transparent cells. Only the guard cells contain chloroplasts. Many stomata may be present. A waxy cuticle can also be found in some leaves.
Draw, label and annotate the structure of a chloroplast.
Each chloroplast is a biconvex disc 3-10 micrometers in diameter.
The chloroplast is surrounded by an envelope of 2 phospholipid membranes which are permeable to glucose, Mg²+, CO2, O2.
There is a system of membranes running through the stroma. These consist of flattened fluid filled sacs or thylakoids which can form stacks in some areas. A single stack is called a granum, many stacks are called grana. Grana can be connected to each other by membranes. Granal membranes present a large surface area for the location of primary and accessory pigments (photosystems), electron carriers, and other chemicals needed for the light dependent reactions.
The stroma is the site of light independent reactions. It contains enzymes eg. RUBISCO (ribulose bisphosphate carboxylase enzyme), sugars, 70s ribosomes, single circular DNA molecule, lipid droplets, starch grains.
