topic 4 plant biology

TOPIC 4

Plant Biology~ SCIENCE 10H ~

Multicellular Organisms

● Cells have to be small to maximize the SA: V ratio

● Unicellular organisms existed on Earth way before multicellular organisms….

● What advantage is there to being multicellular?

Advantages of Multicellularity

Division of Labour

Cells may become specialized to carry out particular functions more efficiently

SizeInternal transport systems created by cells working together allow organisms to be bigger.

Lifetime The death of one cell does not mean the death of the whole organism

Are there any disadvantages of multicellularity?

Plants as Multicellular Organisms

● The same advantages & disadvantages of multicellularity apply to plants.

● Plants have evolved a number of specialized organ systems, cells & tissues to help address the challenges faced by multicellular organisms…

An Introduction to Plant Adaptations…

How Do Plants Do Stuff?

Dermal Tissue

Transpiration

• Transpiration: evaporation of water through the leaf stomata

How Does Water Travel Upwards Against Gravity?

How Does Water Travel Upwards Against Gravity?

Water is transported up the xylem as a result of 4 phenomena:

1) Transpiration pull – water molecules are pulled upwards to the leaves where they will evaporate

2) Root pressure – water enters roots by osmosis, collects, and pushes upward as new water comes in.

How Does Water Travel Upwards Against Gravity?

Water is transported up the xylem as a result of 4 phenomena:

3) Cohesion – the tendency of water molecules to stick to each other

4) Adhesion – the tendency of water molecules to stick to other surfaces

How Do Stomata Open and Close?

Turgid

● Turgid: swole (with water)

● Turgor pressure: the pressure exerted on the cell wall by the osmotic flow of water into the cell.

HIGH turgor

pressure

LOW turgor

pressure

HIGH turgor

pressure

LOW turgor

pressure

Conserving Water1. Water from the roots travels up the xylem and

enters leaf guard cells by osmosis.

2. Guard cells become turgid, causing stomata to OPEN

3. Transpiration (water evaporates through the leaves) & gas exchange occur freely by diffusion

4. Guard cells start to dehydrate and turgor pressure decreases.

5. Guard cells SHRINK causing stomata to CLOSE, thereby conserving water.

Dermal Tissue

1) Dermal tissue (epidermis)

● Dermal cells in the leaves & stem secrete a waxy coating called the cuticle, which acts to prevent water loss and protect the plant from disease

Transpiration

https://www.nature.com/scitable/k

nowledge/library/water-uptake-

and-transport-in-vascular-plants-

103016037

R E V I E W1) What is transpiration? What plant tissues are

required?

2) Are stomata open or closed at night? Why?

3) A plant has extremely low turgor pressure. Are the stomata likely to be open or closed? Explain.

4) How does water enter the roots? How is it carried upwards against gravity?

What fruit/vegetable contains the most sugar??

Plants contain three specialized types of tissues…

1)

2)

3)

PHOTOSYNTHESIS

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Ground Tissue Specializations• Ground tissue is anything that’s not vascular or

dermal. It is also called mesophyll tissue.• There are 2 types of mesophyll tissue:

1) Palisade Mesophyll is the site of photosynthesis; cells are tightly packed and contain TONS of chloroplasts.

2) Spongy Mesophyll facilitates gas exchange; cells are spread out with lots of space in between so gases entering or exiting via the stomata have room to move around.

PHOTOSYNTHESIS

• Photosynthesis is the chemical process plants use to make

sucrose (a type of sugar):

CO2(g) + H2O(g) C6H12O6(s) + O2(g)

How do you think photosynthesis is affected when turgor

pressure is low?

sunlight

LEAF STRUCTURE & PHOTOSYNTHESIS

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Summary: Plant Tissues