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Learning Intentions - Leaves and Photosynthesis
Learning Intentions - Leaves and Photosynthesis
3. Identify and explain the structure and functions of a leaf
Draw a cross section of the leaf and label:
waxy cuticle, epidermis, palisade layer, spongy mesophyll, vascular tissues/bundle (xylem and phloem), stomata and guard cells.
Carry out a leaf tear and view vascular bundles.
Explain the function of the parts that make up a vascular bundle.
Explain how the features of the leaf help the plant to carry photosynthesis and the movement of oxygen, carbon dioxide or water.
Leaf Structure
Leaf Structure
Why are leaves green
Why are leaves green
Leaves are green because the chlorophyll reflects green light
Chlorophyll absorbs Blue and Red light (Infra-red is also reflected)
Chlorophyll is kept small organelles called chloroplasts
There are more chloroplasts, and thus chlorophyll, at the top of a leave than the bottom, this is why the top is greener.
The absorbed blue and red light energy is used by the chloroplasts to split water and carbon dioxide molecules up, they then rejoin to make oxygen and glucose
Have a play with the Virtual Photosynthesis simulator
Change the colour of the light - Red, Green, Blue
What do you notice?
Palisade Mesophyll Cells - Why so upright?
Palisade Mesophyll Cells - Why so upright?
There are 2 types of mesophyll cells - Palisade and Spongy
The Palisade Mesophyll Cells are were most Photosynthesis occurs
They are the top layer of cells after the epidermis
They are at the top of the leaf to get the most light
They are upright to pack as much chloroplast into the space as possible
They are also upright to maximize the surface area for photosynthesis by absorbing most of the light, and reflecting a small amount
In the diagram you can see the advantage to being upright. Any unabsorbed light can bounce (reflect) to the neighbouring cell so it can then be absorbed. A small amount might not be, it will the bounce off to the next cell to be absorbed by the chlorophyll. In the diagram below you will see the change in colour for each reflection - this is to show that only a small amount is reflected with most of the energy being absorbed
Any light that gets past the Palisade Mesophyll Cells will be absorbed by the Spongy Mesophyll Cells which also photosynthesis (just not as much as the Palisade Mesophyll Cells)
Spongy Mesophyll Cells - Where's the Air?
Spongy Mesophyll Cells - Where's the Air?
The haybales are like the mesophyll cells, the space to walk and crawl is like the 'air spaces' in the spongy mesophyll
Leaves are green because the chlorophyll in the chloroplasts absorb Blue and Red light, but green is reflected
This blue and red light energy is used to split water and carbon dioxide molecules up, they then rejoin to make oxygen and glucose
To get the carbon dioxide molecules in to the leave they move through stomata.
To get carbon dioxide from the stomata to the photosynthesizing palisade cells, the carbon dioxide must move through air spaces in the leaf. The area that contains the air spaces is called the spongy mesophyll.
Oxygen created by photosynthesis will also move through the spongy mesophyll and out through the stomata.
With oxygen and carbon dioxide moving through the stomata this is the same, but if reverse to our own breathing. Thus, the stomata is like the nostrils of the plant.
The air spaces are kept open by the network of cells, acting like haybales in a haybale maze - these cells are called the Spongy mesophyll cells
With the leaf getting warm due to the sun, water could evaporate from it, to minimize this, water can only leave through the stomata. Evaporation of the water from the stomata, causes water to then be sucked into the leaf through the straw like xylem, from the roots. This process is called transpiration (like the transport of water through breathing)
To prevent water from leaving through the leave, from any other area, the top of the leaf, where there is the most heat energy, has a waxy layer that water can't get through. This is called the waxy cuticle.
Just like our skin, the outside layer of cells is called the Epidermis
Water gets to the leaf through the xylem.
Sugary water leaves the leaf like fanta, through the phloem.
Leaves are green
Leaves are green
Leaves are green because chlorophyll reflects green light
Chlorophyll absorbs blue and red light and uses this energy for photosynthesis
Infra-red is also reflected
Chloropyll is kept inside of organelles (little organs) inside of the cells called Chloroplasts
Structure of the leaf from the top down
Structure of the leaf from the top down
Cuticle - waxy to prevent water getting out
Epidermis - outside most layer of cells
Mesophyll cells - these are the cells of the leaf
All mesophyll cells contain chloroplasts
Palisade mesophyll - these are at the top of the leaf to capture as much of the sun light as possible, and are the reason that the top of the leaf is more green than the bottom of the leaf. These cells do the photosynthesizing
Spongy mesophyll - these cells do some photosynthesizing. However, their main role is to provide structure to the leaf to allow water and air to move within the leave
Air channels - the spongy mesophyll cells act like the walls of a channel that allows carbon dioxide to diffuse from the air to the palisade mesophyll for photosynthesis
Stomata - these are the nostrils of the leaf. They are underneath the leaf. They are holes. They are made up of 2 Guard cells. The guard cells start to close the stomata if there is not enough water - so they regulate water loss from the plant
Vascular Bundle - contains the Vascular Tissues - Xylem and Phloem
In the Vascular Bundle - Vascular Tissue
In the Vascular Bundle - Vascular Tissue
Like our own Veins and Arteries. The plant has Liquid filled Vessels.
The vessels taking water from the roots up to the leaves are called Xylem
Xylem = zup to the leaves
The vessels taking sugar from the leaves to the rest of the plant are called Phloem
Phloem = flow away
Fanta = sugary drink
Phloem = sugary drink
Fanta = Flow'em = Phloem
Transpiration
Transpiration
Two Vessels: Xylem and Phloem
Two Vessels: Xylem and Phloem
Xylem = Just water = water xylophone
Xylem = Just water = water xylophone
Phloem = Sugar = Fanta = Flow'em
Phloem = Sugar = Fanta = Flow'em
Transpiration process
Transpiration process
Transpiration its like a giant straw
Transpiration its like a giant straw
Water evaporates from the leaves, through the stomata
This causes water to flow from the inner leave closer to the stomata to replace the lost water
This causes water to flow from the Xylem into the leaf
This causes water to flow up the Xylem
This causes water to move from the roots into the Xylem
This causes water to move from the ground into the roots
Transpiration - like combining perspiration and respiration - its the transport of WATER
Translocation is the opposite
Translocation is the opposite
Translocation is how sugar moves from the leaves, through the Phloem, and out to the rest of the plant, to its very tip, and down to its smallest root hair cells
Recap of Learning Intentions - Check you can do all of this
Recap of Learning Intentions - Check you can do all of this
State the structure and function of the leaf
Describe what happens in each part of the leaf
Write the correct photosynthesis equation
Explain photosynthesis and its role in the lifecycle of a plant (Nutrition)
Describe how the environmental conditions affect the rate of photosynthesis (light intensity, temperature and carbon dioxide)
Explain the function of the parts that make up a vascular bundle (Phloem - Translocation of sugar. Xylem - Transpiration of Water)
Discuss how environmental conditions impact the overall survivability of the plant
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