Notes Leaf Structure and Adaptation PDF

Preview

Summary

IGCSE Notes...

Description

Leaf Structure and Adaptation

0

Date: 9th November 2020 LO:

To identify the different parts in leaves of a dicotyledonous plant.

Keywords:

epidermis, waxy cuticle, palisade mesophyll, spongy mesophyll, guard cell, stomata, xylem, phloem

STARTER Use diagram to describe the main stages in making glucose by photosynthesis.

During photosynthesis, plants produce glucose from simple inorganic molecules - carbon dioxide and water - using light energy which drives the chemical reaction. Photosynthesis is a process with two main stages: 1.

Light energy is used to split water, releasing oxygen gas and hydrogen ions.

2.

Carbon dioxide gas combines with the hydrogen to make glucose.

Oxygen is formed as the waste product. Some is used for the plant's respiration, and the rest is released which makes it available for respiration to animals and many microorganisms. Some of the glucose produced by photosynthesis is used for respiration. Glucose is the starting point for the biosynthesis* of materials that plants need to live. 1

(biosynthesis - The production of more complex molecules, from simpler ones, in living organisms)

LEAF STRUCTURE:

2

3D CROSS SECTION OF A LEAF:

LEAF STRUCTURES – FUNCTIONS The leaf consists of a broad, flat part called the lamina, which is joined to the rest of the plant by a leaf stalk or petiole. Running through the petiole are vascular bundles, which then form the veins in the leaf. Although a leaf looks thin, it is made up of several layers of cells. You can see these if you look at a transverse section (cross-section) of a leaf under a microscope.

3

STRUCTURE Waxy Cuticle

Upper Epidermis

Palisade Mesophyll

FUNCTION        

Spongy Mesophyll

Lower Epidermis

Guard Cell

         

Stomata

    

Vascular Bundle

  

Xylem



Phloem



made of wax – waterproofing the leaf (protects layer on the top of the leaf to prevent evaporation) secreted by cells of the upper epidermis thin and transparent – allows light to pass through no chloroplasts are present acts as a barrier to disease organisms main region for photosynthesis cells are columnar (quite long) and packed with chloroplasts to trap light energy receive CO2 by diffusion from air spaces in the spongy mesophyll cells are more spherical and loosely packed contain chloroplasts, but not as many as in palisade cells air spaces between cells allow gaseous exchange – CO2 to the cells, O2 from the cells during photosynthesis acts as a protective layer stomata are present to regulate the loss of water vapour (transpiration) site of gaseous exchange into and out of the leaf also has the guard cells They help to regulate the rate of transpiration by opening and closing the stomata. allowing gas exchange and controlling water loss within the leaf each stomata is surrounded by a pair of guard cells guard cells – control whether the stoma is open or closed water vapour passes out during transpiration CO2 diffuses in and O2 diffuses out during photosynthesis Found in much greater concentration on the underside of the leaf to prevent water loss this is a leaf vein, made up of xylem and phloem xylem vessels bring water and minerals to the leaf phloem vessels transport sugars and amino acids away (translocation) Xylem is the specialized tissue of vascular plants that transports water and nutrients, from the plant-soil interface, to stems and leaves, and provides mechanical support and storage. Transports sugars and amino acids around the plant

4

5

LEAF STRUCTURE - ADAPATATION

6

7

Investigating Photosynthesis –Testing the presence of starch in a leaf A plant was left in the dark for 24 hours and then it was placed in bright light for 6 hours. Then the leaf was taken from the plant and boiled in a liquid to remove the green chemical. • Name the liquid in which the leaf was boiled. Ethanol An iodine solution was then poured onto the ‘white’ leaf and the leaf became blue/black in colour. • What does this result tell us about the green leaf? This result determines the presence of starch.

Before this lesson I already knew how to test presence of starch in a leaf. One thing I must remember from today’s lesson is that plants photosynthesise only during the day. Today I have learnt that plants transpire and respire day and night.

8...