Plant tissue, Photosynthesis, Plant diseases

Epidermal tissue

• Secretes a waxy substance

• waterproofs and protects the surface of the plant

Palisade Mesophyll

• contains lots of chloroplasts

• allows for photosynthesis to take place

spongy mesophyll

• contains big spaces

• large surface area for diffusion of gases

stomata / guard cells

• stomata is opened and closed by guard cells

• allows for diffusion of gases and water loss to take place

meristem tissue

• stem cells that can differentiate

• found on tips of roots and shoots which help their growth

What are xylem and phloem?

Transport tissues in a plant

How does temperature affect transpiration?


Higher temperatures increase the rate

What is the structure and function of xylem tissue?


• Made of dead cells connected end to end

• One-way system for water transport

• Contains a central space called lumen

• Transports water from roots to leaves

What is the role of xylem in plants?

• Transports water and minerals from soil to leaves

• Water travels up the lumen by transpiration

• Supports photosynthesis

What are xylem walls made of?


Lignin (which helps it handle pressure changes)

What is transpiration in plants?

• Movement of water from roots to leaves

• Water evaporates at the leaf surface

• Flow of water is known as transpiration stream

How light affects transpiration

• bright light increases rate

• stomata opens wider to allow more CO2 into the leaf for photosynthesis

How temperature affects transpiration

• faster in higher temperatures

• evaporation and diffusion are easier in higher temperatures

How wind affects transpiration

• faster in windy conditions

• water vapour near stomata is removed quickly speeding up diffusion of water vapour out of leaf

How humidity affects transpiration

• slower in humid conditions

• diffusion of water vapour out of leaf slows down if surrounded by moist air

Potometer

• used to measure transpiration

• water loss from apparatus is via transpiration

• as water moves up the plant the bubble moves along the scale giving a measure of water absorbed by the plant over time → transpiration rate

What is the function of phloem tissue in plants?

• Carries food made by photosynthesis from leaves to the rest of the plant

• Moves sugars through translocation

translocation

• the process of movement of dissolved sugars

• can move sugars up and down the plant

What is the composition of phloem?

• cell walls made of cellulose

• cells are arranged end to end

• cell wall has holes called sieves which allows cytoplasm from one cell to extend to the other cell

What is the chemical equation for photosynthesis?


6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Photosynthesis

• process of making glucose

• light energy from sun is converted to chemical energy in glucose

• endothermic

• takes place in chloroplasts because chlorophyll pigment absorbs light

What role do stomata play in photosynthesis?


They allow carbon dioxide to enter

What is the role of glucose in plants?

It is used to make cellulose

What do plants store for long-term energy?

Starch

What are the limiting factors of photosynthesis?

• Carbon dioxide concentration

• Light intensity

• Temperature

Carbon Dioxide concentration

•The rate of photosynthesis   increases steadily initially as the concentration of CO₂ increases.

• After a while, the rate of photosynthesis does not increase, even though there is an increase in the concentration of CO₂

•The graph plateaus as raising CO₂ will no longer have an effect on photosynthesis and therefore it is no longer a limiting factor.

Light intensity

•The rate of photosynthesis   increases steadily initially as the intensity of light increases.

• After a while, the rate of photosynthesis does not increase, even though there is an increase in the intensity of light.

•The graph plateaus as raising light intensity will no longer have an effect on photosynthesis and therefore it is no longer a limiting factor.

Temperature

• The rate of photosynthesis   increases steadily as temperature increases.

• Enzymes have increased kinetic energy and more successful collisions occur

• The highest rate of photosynthesis is achieved at the optimum temperature.

• At higher temperatures, there is denaturing of the enzymes, which leads to a decrease in the rate of photosynthesis.

How CO2 is used as a limiting factor

•Burning of propane produces carbon dioxide in greenhouse

How light is used as a limiting factor

•Sunlight gets in through glass

•Light switched on at night

How temperature is used a s a limiting factor

•Greenhouse trap heat energy from sunlight

•Heating and cooling systems keep greenhouses at optimum temperature

•Air circulation system keeps heat evenly distributed

Deficiency disease

• Lack of nitrates = not enough protein in plants = reduced growth in plants = stunted growth

• Lack of magnesium ions = not enough chlorophyll made in plants = reduced photosynthesis = chlorosis. Plants would look yellow

Diseases caused by pathogens and pests

• Aphids found on plants can cause huge damage

• TMV caused by viruses

• Rose black spot caused by fungi

How to detect plant disease

1.Stunted growth

2.Spots on leaves

3.Patches of decay

4.Abnormal growths (lumps)

5.Discolouration

6.Malformed stems or leaves

7.Presence of pests

Physical plant defences

• Thick waxy cuticle which acts as a barrier to pathogens

• Cell wall made out of cellulose which is tough and difficult for pathogens to enter

• Dead cells layers on their stem/bark which acts as a barrier to pathogens

Chemical plant defences

• Anti-bacterial chemicals which can kill bacteria

• Poisons produced to deter herbivores (plant eaters)

Mechanical plant defences

–Thorns and hairs – deters animals

–Leaves that droop or curl when touched

–Mimics animals

–Passion flower has bright yellow spots which looks like butterfly eggs; this stops other butterflies from laying their eggs there

Describe two ways the gardener could identify a plant disease.

• compare symptom with gardening manual

• use monocional antibodies test