Lesson Plan

5. Describe the structure of a leaf

KS3-16-05

Intent

Lesson Intention

  • Explain how leaves have adapted to enable photosynthesis
  • Identify and explain the functions of the different cells in a leaf

National Curriculum

  • The adaptations of leaves for photosynthesis

Working Scientifically

  • Use appropriate techniques, apparatus, and materials during fieldwork and laboratory work, paying attention to health and safety
  • Make and record observations and measurements using a range of methods for different investigations; and evaluate the reliability of methods and suggest possible improvements

Learning Outcomes

  • Explain how leaves have adapted to enable photosynthesis
  • Identify and explain the functions of the different cells in a leaf
  • Follow a method to collect a sample from a leaf and then view under a microscope

Resources

Resources: Clear nail varnish, clear sticky tape, deciduous leaves, microscope, microscope slides.

Handout: An investigation sheet for the students to complete.

Rocket words

  • mesophyll
  • epidermis
  • palisade cells
  • stomata
  • waxy cuticle

Implementation

Prior Learning: 

Use lessons 1 and 2 to recap on the role of the stomata and the structure of plant cells.

Starter

Ask the students: What do plants use their leaves for?

Main Teaching

Use the presentation slides to explain the structure and purpose of the different parts of a leaf, including the upper epidermis, the mesophyll, the stomata and the lower epidermis. Emphasise how photosynthesis occurs in the chloroplasts, which are located in the mesophyll. Then, recap and go into further detail on the role of the stomata, xylem and phloem. You may wish to pause the presentation regularly to consolidate new vocabulary. Answer any questions during the presentation and then take samples of leaves to view under a microscope.

Career Film: Liam Anderson works as a Team Leader at the RHS.

Expert Film: This is Liam Anderson, who works as a Team Leader at the RHS. Liam talks about the structure of a leaf.

Mission Assignment

Visualising stomata

Students will examine the top and bottom structures of a leaf under a microscope. This method is used as leaves are typically too opaque to examine under a microscope.

  1. Pick a fresh flat leaf and paint a small section on the top and bottom of the leaf with nail varnish; then, leave it to dry.
  2. Once the varnish is dry, place a piece of sticky tape over the varnish and peel it off.
  3. Stick the tape directly over the microscope slide.
  4. Place the slide on the microscope to examine it.

Students then draw what they see on the handout.

Differentiated tasks (Support/Challenge)

Support: Ask the students to research different plants and their leaves - how do the leaves help the plants to survive?

Challenge: Ask the students to research how plants are adapted to dry environments like the desert - what are their leaves like?

Impact & Assessment Opportunities

Plenary

Discuss the students’ results from the challenge or support tasks. What other environments which require plants to adapt can the students remember? They can also review the keywords and add them to their unit keywords sheet.

Teacher Mastery

The Science Behind the Science

leaf struture cuticle mesophyll stoma

Upper Epidermis: this is the tissue on the upper surface of the leaf. It produces a waxy layer, called the cuticle, which is not made of cells but is a waterproof barrier to prevent excessive evaporation through the hot upper surface of the leaf. The upper epidermis cells have no chloroplasts, so light passes through them easily.

Palisade Mesophyll: this tissue is where 80% of the photosynthesis takes place in the leaf. The palisade cells have many chloroplasts in their cytoplasm and the box-like shape and arrangement of these cells ensures they are packed tightly together.

Spongy Mesophyll: this tissue contains large air spaces that are linked to the atmosphere outside the leaf through microscopic pores called stomata on the lower surface. Spongy mesophyll cells also contain chloroplasts and photosynthesis occurs here too. The air spaces reduce the distance carbon dioxide has to diffuse to get into the mesophyll cells and the fact that these cells have fairly thin cell walls which are coated with a film of water together means that gas exchange between the air space and mesophyll is sped up.

The Lower Epidermis: this contains specialised cells called guard cells which enclose a pore called a stoma. Carbon dioxide can diffuse into the leaf through the stomata when they are open (usually at day time) and water evaporates out of the stomata in a process called transpiration.

Adaptations of a Leaf for Photosynthesis:

  • Large Surface Area – to maximise light harvesting
  • Thin – to reduce distance for carbon dioxide to diffuse through the leaf and to ensure light penetrates the middle of the leaf
  • Air Spaces – to reduce distance for carbon dioxide to diffuse and to increase the surface area of the gas exchange surface inside the leaf
  • Stomata – pores to allow carbon dioxide to diffuse into the leaf and water to evaporate out (transpiration)
  • Presence of Veins – veins contain xylem tissue (carries water and minerals to the leaf from the roots) and phloem (transports sugars and amino acids away from the leaf)
  • Chloroplasts – mesophyll cells and guard cells contain many chloroplasts. These organelles contain the light-harvesting pigment chlorophyll and are where all the reactions of photosynthesis occur