Inside a leaf: structure and function
A cross-section of a dicotyledonous leaf: cuticle, epidermis, palisade and spongy mesophyll, vascular bundle with xylem and phloem, stomata and guard cells, and what each one does. With Vietnamese subtitles. A “Check yourself” section with typed questions is below the video on the site.
Practice
- Check yourself: Inside a leaf: structure and function – Type the missing words, put the steps in order and write a short answer. No multiple choice: you have to remember it. Vietnamese help for every question.
Transcript
A leaf is thin and flat. This gives a large surface area to absorb light, and a short distance for gases to travel. To look inside, we cut across the leaf and study the cross-section.
At the top is the cuticle. It is a waxy layer that stops water loss. Below it is the upper epidermis. Its cells are transparent, so light passes through.
Next is the palisade mesophyll. These cells are tall and packed with chloroplasts. So most photosynthesis happens here.
Below is the spongy mesophyll. These cells are loosely packed, with air spaces between them. Gases, such as carbon dioxide, diffuse through the air spaces.
The vascular bundle contains the xylem and the phloem. The xylem brings water and gives support. The phloem carries sugars away.
At the bottom is the lower epidermis, with tiny holes called stomata. Two guard cells open and close each stoma. Carbon dioxide enters, and oxygen leaves, through the stomata.
Each structure matches its function. The palisade cells have many chloroplasts near the top, to absorb the most light. The stomata and air spaces let carbon dioxide reach the cells.
The xylem brings water to the leaf for photosynthesis, and also gives support. The phloem carries the sugars away to the rest of the plant.
Remember. The cuticle and the epidermis protect the leaf and let light through. The palisade mesophyll does most photosynthesis. The spongy mesophyll and stomata are for gas exchange. And the xylem and phloem transport water and sugars.
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