Life Processes at the Cellular Level - bio

What is the overall equation for photosynthesis?

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ Light energy and chlorophyll are required

Where does the light-dependent reaction occur?

In the thylakoid membranes/grana of the chloroplast.

Where does the light-independent reaction occur?

In the stroma of the chloroplast.

What happens during the light-dependent reaction?

Chlorophyll absorbs light energy. Water is split, producing oxygen, hydrogen ions and electrons, and energy is captured in molecules such as ATP.

Why are grana useful for photosynthesis?

Grana contain stacked thylakoid membranes, providing a large surface area containing chlorophyll. This maximises light absorption, increasing the rate of the light-dependent reactions and therefore increasing the energy available for glucose production.

Why is chlorophyll important?

Chlorophyll absorbs light energy. This energy excites electrons and provides the energy needed to drive the light-dependent reactions.

Why are the light-dependent and light-independent reactions linked?

The light-dependent reaction captures light energy and produces energy-rich molecules. These provide the energy needed for the light-independent reaction to convert CO₂ into carbohydrates. Therefore, without the light-dependent reaction, carbohydrate production is greatly reduced.

Why does CO₂ concentration affect photosynthesis?

CO₂ is a reactant in the light-independent reaction. Increasing CO₂ availability can increase the rate of carbon fixation and therefore glucose production, until another factor becomes limiting

Why does light intensity affect photosynthesis?

Increasing light intensity provides more energy for the light-dependent reactions, increasing ATP production and potentially increasing the rate of carbohydrate production. However, once another factor becomes limiting, further increases in light intensity have little effect.

Why does temperature affect photosynthesis?

Many reactions involved in photosynthesis are enzyme-controlled. Increasing temperature initially increases kinetic energy and collision frequency, increasing reaction rate. Above the optimum, enzymes can lose their functional shape, reducing photosynthesis.

What is the overall equation for aerobic respiration?

Glucose + oxygen → carbon dioxide + water + ATP

What is the main purpose of cellular respiration?

To release energy from glucose and transfer it into ATP, which can be used to power cellular processes.

What is glycolysis?

The first stage of respiration, where glucose is broken down into smaller molecules, producing some ATP.

What happens when oxygen is available?

Aerobic respiration can continue, allowing much more ATP to be produced from glucose.

What happens when oxygen is unavailable?

Cells can use anaerobic respiration/fermentation to regenerate molecules needed for glycolysis, allowing some ATP production to continue, but much less energy is obtained per glucose molecule.

Why does anaerobic respiration produce less ATP?

Glucose is only partially broken down, so much of its chemical energy remains in the products. Aerobic respiration allows more complete oxidation of glucose and therefore produces substantially more ATP.

What is an enzyme?

A biological catalyst, usually a protein, that increases the rate of a reaction without being consumed.

What is the active site?

The region of an enzyme where the substrate binds and the reaction occurs.

What is the induced-fit model?

The active site changes shape slightly when the substrate binds, allowing the enzyme and substrate to interact effectively and lowering the activation energy.

How does temperature affect enzyme activity?

increasing temperature generally increases molecular movement and successful collisions, increasing reaction rate up to the optimum. Above the optimum, bonds maintaining the enzyme's structure can be disrupted, changing the active site so the substrate no longer fits effectively.

How does pH affect enzyme activity?

Changes in pH can alter interactions between amino acids that maintain the enzyme's shape. Extreme pH can change the active site, reducing substrate binding and therefore enzyme activity.

What is a competitive inhibitor?

A molecule that competes with the substrate for the enzyme's active site. Increasing substrate concentration can reduce its effect because more substrate molecules compete for the active sites.

What is diffusion?

Net movement of particles from an area of high concentration to low concentration, down the concentration gradient.

What is osmosis?

Net movement of water across a selectively permeable membrane from a region of higher water potential/lower solute concentration to lower water potential/higher solute concentration.

What is facilitated diffusion?

Passive movement of substances down their concentration gradient through membrane proteins.

What is active transport?

Movement of substances against their concentration gradient using energy, usually ATP, and membrane transport proteins.

Why is active transport important to cells?

It allows cells to accumulate substances even when their concentration is already higher inside the cell. This maintains concentration gradients needed for cellular functions.

Why do cells divide?

For growth, repair, replacement of damaged cells and, in some organisms, asexual reproduction.

What is DNA replication?

The process of copying DNA before cell division.

Why is complementary base pairing important during DNA replication?

A acts as a template for T, while C acts as a template for G. This allows the original DNA sequence to be accurately copied, ensuring daughter cells receive the necessary genetic information.