Bio - Leaves

Leaf margin

The outer edge of the leaf. May have spikes or a rough edges to stop animals from eating them

Lamina

The surface that is positioned to receive sunlight

Leaf veins

Carries water to all parts of the leaf and collect and carry away the food made in the leaf cells

Main rib

Provides support for the leaf ensuring it stays straight

Petiole

Attaches leaf to the stem of the plant

Waxy cuticle

A waxy layer found on the upper surface of leaves that reduces water loss from the leaf. It is transparent to allow light to penetrate through

Epidermis

These cells are found on the upper and lower surface of the leaf. They support the leaf and protect the leaf from physical damage. They are transparent to allow light to pass through them.

Palisade layer

Tightly packed rectangular shaped cells that contain lots of chloroplasts. This is the main site of photosynthesis

Spongy layer

Loosely packed circular shaped cells that also contain chloroplasts and carry out photosynthesis. They have less chloroplasts per cell compared to palisade cells. This layer also has air spaces which allows gases to diffuse rapidly through the mesophyll so that cells can carry out photosynthesis.

Veins

They are found in the spongy layer. Each vein has thick walled Xylem which carry water to the leaf and Phloem tubes which carry glucose from the leaf and to other parts of the plant that cant make glucose

Stomata

Pores commonly found on the underside of the leaf which allow gases to enter (carbon dioxide) and leave (Oxygen, Water Vapor) the leaf

Guard cells

Cells that change shape and control the size of the stomata. They also contain some chloroplasts and carry out small amounts of photosynthesis

What is the Mesophyll

The mesophyll is the middle part of a leaf, made up of the palisade layer (for photosynthesis) and the spongy layer (for gas exchange). It lies between the upper and lower epidermis and is where most of the leaf's photosynthesis happens.

Why is it important for guard cells to control to size of the stomata

Because when the stomata is open it loses water due to evaporation from the hot sun and if it loses to much it could die

What is diffusion

The movement of carbon dioxide from high concentration (in the air) to an area of low concentration (in the leaf)

What times of the day does the stomata normally open

The opens during the and closes at night however stomata may close in bright sunlight in hot, dry conditions why water conservation is a matter of life or death

Photosynthesis equation

sunlight

Carbon dioxide + water --------> glucose + oxygen

chlorophyll

How do u test a leaf for starch

Place leaf in boiling water for 30sec (removes waxy cuticle), Boil the leaf in ethanol for a few min (to remove the chlorophyll), wash the leaf(to remove the meths), add Iodine solution to the leaf(to test for starch)

Color meaning from iodine test

Blue-black: starch is present goes brown because of iodine or doesn't change color: no starch is present

Which factors limit the rate of photosynthesis

Light intensity Concentration of carbon dioxide Wavelengths of light

How is wavelengths a limiting factor

Leaves are green because the reflect green (and sometimes yellow) wavelengths of light meaning they cant absorb them however other wavelengths of light such as purple, blue and red can be absorbed and used for photosynthesis. If a plant is only given green wavelengths of light it can photosynthesise because it reflects the green wavelength of light

How is light intensity a limiting factor

The higher the light intensity, the faster the rate of photosynthesis until other factors begins to limit it due to limited supply

How is carbon dioxide concentration a limiting factor

Carbon dioxide is a limiting factor when its concentration is too low to support the maximum rate of photosynthesis. If it is increased the rate of photosynthesis increases until other factors begin to limit the rate.

How can we measure photosynthesis

by the rate O2 is produced

What is stratification

a pattern which shows vertical layering eg seen in forest ecosystems

What are the layers in stratification

Emergent layer: The tallest trees that rise above the general canopy Canopy Layer: The main layer of trees that form the roof of the forest. Understory: Made up of smaller trees and shrubs that grow beneath the canopy. Shrub Layer: Consists of woody plants and shrubs. Ground layer: Grasses, ferns, and small plants on the forest floor.

What is a shade and non-shade plant

Non-shade plants are plants exposed to high light intensity while shade plants are only exposed to low light intensity

How do non-shade plants differ to shade plants

Non-shade plants

-smaller surface area (They do not need as big SA to absorb light since they already are exposed to high light intensity. Small SA protects the leaf from absorbing to much light and losing to much water by evaporation)

-dense and thick leaves (A thicker leaf can have more palisade layers allowing it to capture high levels of light energy effciently) -light green (Fewer chlorophyll and chloroplasts in palisade layer. Due to high light intensity each leaf does not need large amounts of chlorophyll to absorb light) -many stomata (high light intensity results in more photosynthesis. High rate of photosynthesis requires more CO2 so it can take place)

How do shade plants differ to non-shade plants

Shade plants -large surface area (They are expose to low light intensity so they need a large SA to absorb as much light as possible.) -less dense, thin leaves (Low light intensity cannot easily penetrate the leaf. A thinner leaf allows low light intensity to penetrate not just palisade layer but also spongy layer) -dark green (More chlorophyll and chloroplasts spread across the leaf. Because of low light intensity each leaf needs to maximise abiltiy to recieve sunlight.) -fewer stomata (Lower levels of light intensity results in a lower rate of photosynthesis. Lower rate of photosynthesis requires less CO2 so less stomata overall.)

Osmosis definition

Osmosis is the movement of water from high concentration to low concentration through a semi-permeable membrane

What is osmosis

Osmosis is the absorption of water through a plants roots. Roots have root hairs which increase the SA of the roots and allow more water to be absorbed through osmosis

What is the vascular bundle

The vascular bundle consists of the xylem vein and the phloem vein. The xylem vein are dead hollow long thin tubes that allow water to move up the stem. They have thickened walls that help hold the plant up.

What is capillary action

Capillary action is how water moves up the xylem through the process of adhesion and cohesion along with the transpiration pull.

What is adhesion and cohesion

Adhesion is when water molecules stick to the walls of the xylem and cohesion is when water molecules stick to each other. These help transport water up the stem.

What is transpiration

Transpiration is the evaporation of water from the surface of a plant, mainly through the stomata in the leaves because the waxy cuticle is waterproof stopping water from being lost through there.

What is the transpiration pull

The transpiration pull occurs when water is evaporated from the surface of the leaf (transpiration) which creates a suction or pull of water up the xylem to replace the water being lost through evaporation.

What is the structure of a typical fungus

(A) Sporangium: to produce and protect spores (B) Spores: Reproductive cell that will grow into new fungus Sporangiophore: Raises the sporangium upwards, giving it greater exposure to wind, water, animals (C) Hyphae: Feeding structure (D) Mycellium: A large mass of hyphae

How do fungi obtain food

extra-cellular digestion

what is extra-cellular digestion

It occurs when enzymes are secreted form hyphae onto a food source . The food is broken down outside the fungus and then absorbed into the fungus.

Why do fungi need to carry out extra-cellular digestion

Because large food molecules are to big to be absorbed and must be broken down into building blocks which are small enough to be absorbed

How do fungi reproduce sexually

Most fungi can reproduce sexually with mating between different hyphae forming sporangia which form spores with a mixture of genetic material from both parents

How do fungi reproduce asexually

They can either asexually reproduce by creating asexual spores which are genetically identical to the parent or a piece of the hyphae breaks off and grows into a new fungus.

difference between asexual and sexual reproduction

Sexual reproduction is slower but it introduces genetic variation which can be essential to the survival of the fungus species when environmental conditions are changing.

How do fungi grow

Spore germinates to produce hyphae in places where it is moist, warm and has a good food supply.

What kind of relationship does the kauri tree have with mycorrhizal fungi?

Mutualistic (+/+): both benefit.

What do kauri trees give mycorrhizal fungi and what do mycorrhizal fungi give kauri trees in return?

Kauri trees give glucose from photosynthesis (up to 20% of production) and in return they recieve help with water absorption via fine hyphae that increase root surface area.

Why can't mycorrhizal fungi perform extracellular digestion?

They evolved to rely entirely on the kauri for nutrition.

What organism causes kauri dieback disease?

Phytophthora agathidicida, an oomycete.

How does Phytophthora agathidicida feed?

Using extracellular digestion to break down kauri root cells and vasculature.

What happens when kauri trees can't transport water to their leaves?

Photosynthesis stops → no glucose → no energy → death.

What's the first stage of kauri infection?

Oospores arrive in soil; in moist conditions, they release swimming zoospores.

What happens after zoospores reach the roots?

They form cysts → hyphae → mycelium that invades root cells and follows water/sugar pathways.

What's the final effect of the infection?

The tree's roots and branches die due to cell death and loss of water/photosynthesis.

How are oomycetes similar to fungi?

Both have hyphae, extracellular digestion, and reproduce with spores.

How are oomycetes different from fungi?

Oomycetes have cellulose in their cell walls (not chitin) and use two spore types: oospores & zoospores.

What are the key symptoms of kauri dieback?

Bleeding gum, yellowing leaves, thinning canopy, and dead branches.

Why do leaves yellow and fall off?

No water = no photosynthesis = no chlorophyll.

Is there a cure for kauri dieback?

No. The only solution is prevention and limiting spread.

How do zoospores spread the disease?

By swimming ~3m/year in moist soil; only within infected groves.

What spreads the disease between forests?

Oospores in contaminated soil moved by humans or pigs.

What is a rāhui?

A traditional Māori ban to protect natural areas by restricting access.

What is the most effective disinfectant?

Sterigene - kills zoospores on contact, weakens oospores, and destroys mycelium in 8 days.

Why is brushing off soil essential before and after forest visits?

Disinfectants can't kill oospores deep in soil, so physical removal is critical.

How long can oospores survive in soil and can they move

Up to 3 years or more and no they cant move

What happens when oospores germinate?

They produce sporangia, which then release zoospores.

How long do zoospores live?

Only a few days — they are short-lived.

What is the role of zoospores in spreading kauri dieback?

They spread the disease within already infected kauri groves, but not between distant forests.