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Georgia Lofts

Georgia Lofts

Email: georgialofts@gmail.com

Total Article : 144

About Me:I am a second year student studying BioMedical Science. I am interested in a wide range of topics but particularly like to focus on Biology, Art and Philosophy.

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GCSE Revision: Organisation and Plant Tissues

GCSE Revision: Organisation and Plant Tissues

GCSE BIOLOGY REVISION: ORGANISATION AND PLANT TISSUES

 

 

Principles of organisation

 

Cells are the basic building blocks of all living organisms.

 

A tissue is a group of cells with a similar structure and function.

 

 Organs are aggregations of tissues performing specific functions.

 

Organs are organised into organ systems, which work together to form organisms.

 

Students should be able to develop an understanding of size and scale in relation to cells, tissues, organs and systems.

 

These concepts have been discussed in further details in a previous article.

 

Plant tissues

 

Students should be able to explain how the structures of plant tissues are related to their functions.

Plant tissues include:

• epidermal tissues

 • palisade mesophyll

• spongy mesophyll

• xylem and phloem

 • meristem tissue found at the growing tips of shoots and roots.

 

The leaf is a plant organ. Knowledge limited to epidermis, palisade and spongy mesophyll, xylem and phloem, and guard cells surrounding stomata.

 

Tissue

Structure relating to function

Epidermal tissue

Thin and transparent. This allows more light to reach into the palisade cells

Palisade mesophyll

Absorption of more light and the increased rate of photosynthesis

Spongy mesophyll

There are air spaces inside which allow carbon dioxide to diffuse through for photosynthesis

Xylem and phloem

Xylem- lose their end walls so a continuous hollow tube is formed. Walls are strong with lignin deposition as lignin gives strength and support

Phloem- presence of companion cells to carry out the living functions of the cell. Has sieve tubes which are specialised for transport as they have no nuclei, this means there is more room for movement of solutes. Additionally, cytoplasm connects from one cell to the next.

Meristem tissue

Undifferentiated cells, able to develop into whatever type of cell is required in the plant

 

 

Structure of the leaf and its adaptations for photosynthesis (top to bottom of leaf)

 

Structure

Purpose

Adaptations

Waxy cuticle

Makes the leaf waterproof

-

Upper Epidermis

Provides a layer for the waxy cuticle to lie on

Thin and transparent to maximise the amount of light which can reach the mesophyll layers

Palisade Mesophyll

Photosynthesis

The cells in this layer contain many chloroplasts to maximise the rate of photosynthesis

The cells are column shaped and packed closely together to maximise the number of cells that can be packed into this layer and so maximise the rate of photosynthesis

Layer situated towards the upper surface of the leaf so that the photosynthesising cells are close to the light

Spongy Mesophyll

Gas exchange and photosynthesis

 

Gas exchange is where carbon dioxide diffuses into the spongy mesophyll cells, and oxygen diffuses out. This is vital for photosynthesis (see later topic)

Layer packed loosely so that gases can get between the cells.

Cells covered by a thin layer of water which the gases dissolve in as they move into and out of cells.

Cells also contain chloroplasts for photosynthesis but less than the palisade layer.

Lower epidermis

Provides a layer for the waxy cuticle to lie on

Has small pores called stomata which allow water to enter or exit the leaf by transpiration. Guard cells open and close the stomata to control the rate of transpiration and so water loss.

 

image- https://www.holganix.com/blog/plant-tissue-is-cooler-than-you-think

 

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