CASE STUDY SCENARIO In order to discuss plants in a meaningful way, it is important to know the proper names for all the different parts a plant can have. Flowering plants have four major part types: Leaves Flowers Stems Roots Leaves Leaves make all the food for the plant. They do this by changing light, water and gases into food. This process is called photosynthesis. How are the leaves structurally adapted as photosynthesizing organs?

EXTERNAL STRUCTURE This refers to the morphology of the leaf(outer side) All leaves are responsible for: absorbing the sun's rays the majority of photosynthetic production (which can take place in any green part of a plant), taking in carbon dioxide and releasing oxygen and water vapor (breathing) removing waste products from the plant using osmotic pressure to draw water up from the roots PARTS OF A LEAF Tip of the terminal point of the leaf is the leaf Apex. Lamina the flattened, green, expanded portion of a leaf. Margin edge of a leaf.  Midrib the most prominent central vein in a leaf.  Lateral veins secondary veins in a leaf.  Petiole the leaf stalk (connects blade to stem).

INTERNAL STRUCTURE The leaf is covered by two layers. The Upper epidermis and the Lower epidermis. Between these two layers is a Mesophyll tissue layer made up of the Palisade cells and the spongy cells.

• Cuticle: - Is non-cellular, water proof and transparent • Cuticle: - Is non-cellular, water proof and transparent. It allows light to pass through. • Upper epidermis: - Is a single layer of cells on the upper surface of a leaf. It allows light to pass to the cells below. • Palisade mesophyll: - has cells vertically arranged such that many can fit into a small space. The cells have large number of chloroplasts. • Chloroplasts:- contain chlorophyll for absorbing sunlight. • Spongy mesophyll: - Have large air spaces for fast diffusion of gases to and from the photosynthesizing cells. The cells have few chloroplasts. • Veins (Vascular bundles): - They act as drain pipes distributing raw materials to the leaves and conducting away manufactured food to other parts of a plant. • Stoma: - A pore that allows gaseous exchange to take place. Carbon dioxide enters and oxygen leaves the leaf through stomata. • Thin lamina: - Provides a short distance over which diffusion of gases take place. • Broad lamina: - Some leaves have a broad lamina which provides a large surface area for absorbing sunlight energy.

EXCERCISES QUESTION 1 Name 4 main parts of the leaf Which of these above mentioned parts serve a vital role for photosynthesis? QUESTION 2 Fill in the missing words • ---------- Is non-cellular, water proof and transparent. It allows light to pass through. • ---------------- Is a single layer of cells on the upper surface of a leaf. It allows light to pass to the cells below. • ----------------- has cells vertically arranged such that many can fit into a small space. The cells have large number of chloroplasts. • ---------------- contain chlorophyll for absorbing sunlight. • ---------------- Have large air spaces for fast diffusion of gases to and from the photosynthesizing cells. The cells have few chloroplasts. • ---------------- A pore that allows gaseous exchange to take place. Carbon dioxide enters and oxygen leaves the leaf through stomata.

References 1.Mckean D.G (1973), introduction to Biology, Hodder Murry (UK) London. 2. Ian J. Burton (2001), the Cambridge Revision Guide GCE, level Biology,     Cambridge University Press. 3.Maxwell – Ojo.B (1998), Modern Tropical Biology, Evans and Brothers London(UK) 4.Stone R.H and Cozens A. B. (2002), New Tropical Biology (3rd Edition)     Longmans, London (UK).