aqa gcse bioenergetics

What is the word equation for photosynthesis?

Carbon dioxide + water → Glucose + oxygen (light above and chlorophyll under the arrow)

What does the cell wall do?

Provides structure and support to the celll

What is the transpiration stream?

The continuous movement of water up the stem

What is the balanced symbol equation for photosynthesis?

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (light above and chlorophyll under the arrow)

What is photosynthesis?

An endothermic reaction used by plants to produce glucose

What is an endothermic reaction?

A reaction which uses energy from its surroundings

What are the limiting factors of photosynthesis?

Light intensity, temperature, amount of chlorophyll, CO₂ concentration

How does light intensity affect photosynthesis?

As the light intensity increases, so does the rate of photosynthesis because the light transfers the energy needed for photosynthesis.

How does CO₂ concentration affect photosynthesis?

The rate of photosynthesis increases as the concentration of carbon dioxide does, because it is a reactant.

How does temperature affect photosynthesis?

As the temperature increases, enzymes gain kinetic energy and have more successful collisions between enzymes and substrates, creating enzyme-substrate complexes, which increases the rate of photosynthesis. However, after passing the optimum temperature, the enzymes denature and the rate of photosynthesis decreases.

How does the amount of chlorophyll affect photosynthesis?

The chlorophyll absorbs the light energy required for the reaction, so more chlorophyll leads to a higher rate of photosynthesis.

How do you measure the rate of photosynthesis?

By measuring the rate of production of oxygen

How do you calculate light intensity?

By using the inverse square law and multiplying by 10⁴

What is the inverse square law?

1/distance²

What are the uses of glucose produced by photosynthesis?

Respiration, converted into insoluble starch or lipids for storage or cellulose for cell walls, combined with nitrate ions to make amino acids which are used for photosynthesis

What are the 3 main plant organs and their functions?

Leaves - carry out photosynthesis. Stems - support leaves, flowers and fruit. Roots - absorb water and minerals, anchor the plant

What are 3 other plant organs?

Flowers, fruits and seeds

What are the tissues in a plant cell?

Upper epidermis, lower epidermis, palisade mesophyll, spongy mesophyll, xylem, phloem, meristem tissue

What is the function of the waxy cuticle and upper epidermis?

Both are transparent, allowing light to reach photosynthesising cells, and the waxy cuticle is waterproof, protecting against water loss and pathogens

What adaptations do palisade mesophyll cells have for photosynthesis?

Many chloroplasts and closely packed together for more light absorption, located near the top of the leaf, near to the light source.

How does spongy mesophyll facilitate photosynthesis?

It has many air spaces and a large surface area, allowing for faster diffusion of gases (carbon dioxide and oxygen).

What is the role of the vascular bundle in a leaf?

Xylem transports water and minerals from the roots, while phloem transports products of photosynthesis (eg. sucrose and amino acids) to the rest of the plant.

What does the meristem tissue do?

It’s made up of rapidly dividing plant cells, which differentiate into all the other cell types needed, so the plant can grow and replace dead/damaged cells

Where is the meristem tissue found?

At the growing tips of roots and shoots.

What does the stomata do?

Allows for gas exchange to happen. Carbon dioxide goes in, oxygen and water vapour go out. Closes at night to reduce water loss.

How are root hair cells adapted to their function?

They have no chloroplasts as they’re underground, lots of mitochondria to release energy for active transport, large vacuoles containing a concentrated solution to encourage movement of water, increased surface area

What does the xylem do?

Transports water and mineral ions from the roots to photosynthesising cells

What does the phloem do?

Transport products of photosynthesis (such as sucrose and amino acids) to where they’re used or stored

How are xylem vessels adapted to their function?

The lignin spirals give the xylem vessels strength/support, and cause the cells to die and lose their cytoplasms and organelles, so the vessels become dead and hollow

How are phloem vessels adapted to their function?

They have sieve tubes, which have perforated ends and no nuclei, which connect one cell to the next, and companion cells, which provide energy

What is transpiration?

The loss of water from the leaves of a plant

What is translocation?

The transport of sugars and amino acids in the phloem from where they’re produced (sources) to there they’re used/stored (sinks)

What factors affect the rate of transpiration?

Humidity, temperature, light intensity, wind speed

How does light intensity affect transpiration?

Higher light intensity means more stomata are open for gas exchange, leading to a higher rate of photosynthesis (carbon dioxide needed for photosynthesis), so there’s an increased rate of transpiration as water vapour can diffuse out of the stomata

How does temperature affect the rate of transpiration?

Particles have more kinetic energy at a high temperature, so there’s a faster rate of diffusion. There’s also a faster rate of evaporation from spongy mesophyll cells so the rate of transpiration increases

How does humidity affect the rate of transpiration?

A low humidity means a lower concentration of water vapour outside of the leaf, and the difference in concentration leads to a steeper concentration gradient and increased rate of transpiration.

How does wind speed affect transpiration?

Water vapour outside of the leaf pushed away by the wind, so there’s a steeper concentration gradient and a higher rate of transpiration

What are the guard cells called when the stomata is open?

Turgid

What are the guard cells called when the stomata is closed?

Flaccid

What are the two types of respiration?

Aerobic and anaerobic

What do organisms need energy for?

Movement, keeping warm and chemical reactions to build larger molecules from smaller ones

What is aerobic respiration?

Respiration using oxygen

What is anaerobic respiration?

Respiration that does not use oxygen, and releases less energy than aerobic respiration

What is an exothermic reaction?

A chemical reaction that releases energy, such as respiration.

What is the word equation for aerobic respiration?

Glucose + oxygen → Water + carbon dioxide (+ energy in the form of ATP and heat)

What is the chemical equation for aerobic respiration?

C₆H₁₂O₆ + 6O₂ → 6H₂O + 6CO₂

What is the word equation for anaerobic respiration in yeast and plant cells?

Glucose → carbon dioxide + ethanol (+ some energy)

What is the word equation for anaerobic respiration in mammals and some bacteria?

Glucose → lactic acid (+ some energy)

What are the levels of organisation?

Cells, tissues, organs, organ systems

What is a cell?

Basic building blocks and units of an organism (e.g. muscle cells)

What are tissues?

Groups of cells with a similar structure and function (e.g. meristem tissue)

What are organs?

Groups of tissues working together to perform a specific function (e.g. leaves)

What is an organ system?

A group of organs performing specific functions (e.g. digestive system)