Everything till exocytosis

Identify (1–2 marks)

Definition: Recognize and name.
✅ Template:
"[Concept] is [definition]. For example, [example]."

Define (1–2 marks)

Definition: State the precise meaning of a term.
✅ Template:
"[Term] is defined as [concise explanation]."

🔹 Example Question: Define transcription.
✅ Full-Mark Answer:
"Transcription is the process where DNA is used as a template to synthesize messenger RNA (mRNA) in the nucleus."

Describe (2–4 marks)

Definition: Provide characteristics or features.
✅ Template:
"[Concept] involves [key feature 1] and [key feature 2]. This process occurs in [location] and functions to [purpose]."

Explain (3–6 marks)

Definition: Relate cause and effect, why or how something happens.
✅ Template:
"[Concept] occurs because [cause]. This leads to [effect], which results in [outcome]."

Compare (4–6 marks)

Definition: Identify similarities and differences.
✅ Template:
"Both [concept 1] and [concept 2] share [similarity 1] and [similarity 2]. However, [concept 1] differs in that it [difference 1], while [concept 2] [difference 2]."

Analyse (6–8 marks)

Definition: Break down a concept into its components and examine relationships.
✅ Template:
"[Concept] consists of [component 1], [component 2], and [component 3]. The relationship between these is [analysis of how they interact]. This results in [final effect or conclusion]."

Evaluate (6–9 marks)

Definition: Make a judgment based on criteria.
✅ Template:
"The effectiveness of [concept] can be assessed based on [criterion 1] and [criterion 2]. While [advantage 1] supports its use, [limitation 1] presents a challenge. Overall, [final judgment based on evidence]."

Justify (5–8 marks)

Definition: Provide reasons for a choice or decision.
✅ Template:
"[Choice] is the most appropriate because [reason 1] and [reason 2]. Evidence supporting this includes [example or scientific explanation]."

Assess (6–9 marks)

Definition: Make a judgment by weighing evidence.
✅ Template:
"The significance of [concept] can be assessed by considering [factor 1] and [factor 2]. While [positive aspect] demonstrates its effectiveness, [limitation] suggests improvements are needed. Based on the evidence, [final judgment]."

🔹 How to Score Full Marks in Prelim Biology

✔ Use precise scientific terminology
✔ Structure responses logically (PEEL: Point, Explain, Example, Link)
✔ Address all parts of the question
✔ Use examples or experimental evidence when relevant
✔ Write concisely while covering depth

"Discuss" (6–9 marks)

Key Elements of a Full-Mark Response:
✔ Introduction – Define the concept and state the main ideas you'll discuss.
✔ Arguments For (Advantages/Benefits) – Provide supporting evidence.
✔ Arguments Against (Limitations/Challenges) – Provide counterpoints.
✔ Scientific Examples or Evidence – Use real-world applications, data, or experiments.
✔ Conclusion – Summarize the discussion and make a final judgment.

What is the relationship between surface area to volume ratio (SA:V) and cell size?

As cell size increases, SA:V ratio decreases because volume increases faster than surface area.

Why do smaller cells have a higher SA:V ratio?

Smaller cells have a relatively larger surface area compared to their volume, allowing for more efficient diffusion of nutrients and waste.

Why do cells need a high SA:V ratio?

A high SA:V ratio allows for faster diffusion of oxygen, nutrients, and waste removal, ensuring efficient cellular function.

How does SA:V ratio affect gas exchange in organisms?

Organisms with a low SA:V ratio need specialized structures (e.g., alveoli, gills) to increase surface area for efficient gas exchange.

What are ways that cells can increase their surface area to volume (SA:V) ratio?

Cells can increase their SA:V ratio by:

• Being small – Reducing size maintains a high SA:V ratio for efficient diffusion.

• Having a flattened shape – Increases surface area without significantly increasing volume (e.g., red blood cells, flatworms).

• Developing extensions – Structures like microvilli in intestinal cells or root hairs in plants maximize absorption.

• cell compartmentalisation

  allows cells to have separate areas

  with the right conditions for different

  cellular reactions

Describe a prokaryotic cell

• Rhymes with NO

  → NO nucleus, NO membrane-bound organelles

• DNA is single circular chromosome; in a nuceloid or cytoplasm rather than a nucleus

• Can be antotrophic → produce their own food

• Or heterotrophic → relies on other organisms for food

• Cell membrane protected by a cell wall

• Have accessory structures called plasmids and ribosomes.

• Nothing else

Define a cell

The basic structural unit in all organisms

Define cell membrane

A barrier that controls the movement of substances into and out of the cell’s internal environment

Define cytoplasm

The watery fluid within the cell that contains many dissolved substances and faciliates chemical reactions occuring

Define DNA

The main form of genetic material found in a cell, containing instructions for cellular activity

Define ribosomes

A structure within the cell that uses information from genes to produce proteins

Define genes

Consists of DNA and the code for making proteins

Define proteins

Substances provided by the ribosomes wihtin cells, using the code provided by genes

Describe eukaryotic cell

• Rhymes with DO

  → has membrane-bound organelles and nucleus

• DNA in nucleus

• more complex and larger than prokaryotic cells

• linear chromosome

• some are autotrophic and heterotrophic

Define the modern cell theory

The cell is the smallest living unit in all organisms. All living things are made up of cells. All cells come from pre-existing cells.

Identify and Describe the functions of a membrane organelle

• it controls what enters and exits the cell

• allows each organelle to maintain a distinct environment for specific functions

  → different pH levels, ion concentration

• meaning that different reactions can occur in seperate sections without interfering each other

Why is cell compartmentalisation cruical?

• Enzymes and reactants for specific reactions are localised together, therefore improving reaction rates

• processes requiring different conditions can occur simultaneously

• organelles are protected from changes in the environment of a cell

• for efficiency

Compare prokaryotic and eukaryotic cells

Similarities

• cell membrane, cytoplasm

• cell wall (most in pro and some for eu)

• DNA, ribosomes

• genetic material

Prokaryotic

• rhymes with NO

  → NO nucleus, membrane bound organelles

• most have a cell wall

• circular DNA structure

Eukaryotic

• rhymes with DO

  → nucles, membrane bound-organelles

• larger more complex

• DNA in linear structure and in nucleus

Compare between plant and animal cells?

Similarities

• mitochondria, nucleus

• plasma membrane, soft and rough ER

• golgi appartus, ribosomes

Plant Cell

• cell wall, vacoule, chloroplasts

• nucleus usually pushed to the side

Animal Cells

• small vacuoles, centrosomes and centriotes

• cilia or fragella

• nucles usually in center

Idenfity the function of the nucleus

• controls cell activites

• stores genetic information

• DNA replication and DNA synthesis

• occurs in both animal and plant cells

Identify the function of the mitochondria?

• produces ATP, energy, through cellular respiration

• powerhouse of the cell

• present in both plant and animal cells

Define cellular respiration?

Cellular respiration is a biochemical process in which cells convert glucose and oxygen into ATP (adenosine triphosphate), the energy currency of the cell.

identify the function of chloroplasts?

• carries out photosynthesis, convert light, energy → glucose

• contains chlorophyll

• present in plant cells

identify the function of the rough ER (endoplasmic reticulum)?

• synthesis and transports proteins

• covered in ribosomes

• both animal and plant cells

Identify the function of the soft ER (endoplasmic reticulum)?

• synthesis lipids, detoxifices substances and stores calcuim ions

• no ribosomes → smooth

Identify the function of the golgi appartus?

• modifies, sorts, and packages proteins and lipids for storage or transport out of the cell

Identify the function of the lysosomes?

• contains digestive enzymes to break down waste, damaged organelles and foreign substances

• mainly in animal cells

Identify the function of the vacoule?

• stores water, nutrients and waste

• provides structural support in plant cells

  both animal and plant cells

Identify the function of the cell wall?

• provides structure, protection and support

• cellulose in plants and chitin in fungi

Define MR GREEN

Movement, reproduction, growth, response, excretion, exchange of gases, nutrition.

Describe the structure of the cell membrane

The cell membrane

• is a semi-permeable phospholipid bilayer that surrounds the cell

• controlling the movement of substances in and out.

• consists of two layers of phospholipids, with hydrophilic (water-attracting) heads facing outward and hydrophobic (water-repelling) tails facing inward.

• Embedded in the bilayer are proteins (integral & peripheral), cholesterol, glycolipids, and glycoproteins

• is 3D

• contributing to structure and function

Describe the fluid mosaic model

The fluid mosaic model

• describes the structure of the cell membrane as a dynamic, flexible bilayer with proteins and other molecules embedded within it.

• The 'fluid' aspect refers to the movement of phospholipids and proteins

• while the 'mosaic' aspect represents the scattered arrangement of proteins, cholesterol, and carbohydrates."

Define the function of phospholipids in the membrane?

Phospholipids

• form the basic structure of the membrane

• creating a selectively permeable barrier that allows lipid-soluble molecules to pass while blocking water-soluble substances

Define the role of proteins in the cell membrane

Membrane proteins serve various functions:

• Channel & Carrier Proteins: Facilitate transport of molecules.

• Receptor Proteins: Detect and respond to signals like hormones.

• Enzymatic Proteins: Speed up chemical reactions in the membrane.

• Structural Proteins: Provide support and maintain cell shape.

Define the role of cholesterol in the membrane?

Cholesterol is embedded within the membrane and regulates fluidity and stability, preventing the membrane from becoming too rigid in cold temperatures or too fluid in high temperatures

Identify the function of glycoproteins and glycolipids

Glycoproteins and glycolipids have carbohydrate chains attached to them and function in cell recognition, communication, and immune response by acting as 'identification tags' for the cell.

Identify the three main types of transport across the cell membrane?

Transport across the membrane occurs via passive transport, active transport, and bulk transport (endocytosis/exocytosis).

Identify and describe passive transport, and its types?

Passive transport moves substances down their concentration gradient (high to low concentration) without ATP energy. The three types are:

1. Simple Diffusion – Small, nonpolar molecules (O₂, CO₂) diffuse through the bilayer.

2. Facilitated Diffusion – Large or charged molecules (glucose, ions) pass through protein channels or carriers or aquaporins.

3. Osmosis – The movement of water across a semi-permeable membrane from high to low water potential.

Explain selective permeability in relation to the cell membrane

• Selective permeability refers to the ability of the cell membrane to regulate which substances can pass through it.

• The membrane allows certain molecules, like small or nonpolar substances (e.g., oxygen, carbon dioxide), to diffuse freely, while preventing the passage of large, polar, or charged molecules (e.g., glucose, ions) unless they are transported by specific proteins.

• This selective control is vital for maintaining the cell’s internal environment, supporting homeostasis.

Outline the roles of the plasma membrane

The plasma membrane has several essential functions:

1. Selective Permeability: Controls the entry and exit of substances, allowing essential nutrients to enter while removing waste products.

2. Protection and Structure: Acts as a barrier that protects the cell from harmful substances and physical damage while maintaining the cell’s shape.

3. Cell Communication: Contains receptors that allow the cell to respond to external signals, facilitating communication between cells and the environment.

4. Cell Recognition: Glycoproteins and glycolipids on the surface play a key role in the identification and interaction of cells in the immune response and tissue formation.

5. Anchorage: Supports the attachment of the cell to the extracellular matrix and helps anchor the cytoskeleton for structural integrity and mobility.

Distinguish between hydrophilic and hydrophobic and relate this to the structure of a phospholipid.

• Hydrophilic refers to molecules that are attracted to water, while hydrophobic refers to molecules that repel water.

• In a phospholipid, the hydrophilic head (phosphate group) is water-attracting, and the hydrophobic tails (fatty acid chains) are water-repelling. This property of phospholipids is fundamental to the formation of the phospholipid bilayer, where the hydrophilic heads face outward toward water, and the hydrophobic tails face inward, shielded from water.

What is the glycocalyx?

The glycocalyx is a carbohydrate-rich layer that covers the surface of the cell membrane, consisting of glycoproteins and glycolipids. It plays crucial roles in cell recognition, adhesion, and protection. The glycocalyx also helps in immune response by enabling the cell to recognize foreign cells and participate in cell signaling processes.

Explain why the plasma membrane is described as semi-permeable and provide examples of things that can and cannot cross the membrane.

The plasma membrane is semi-permeable because it selectively allows certain substances to pass through while blocking others.

• Can cross: Small, nonpolar molecules like oxygen (O2) and carbon dioxide (CO2) can diffuse freely across the membrane.

• Cannot cross: Large, polar molecules like glucose and charged ions such as sodium (Na+) and potassium (K+) require transport proteins to move across the membrane, as they cannot diffuse through the lipid bilayer.

What is an amphipathic molecule?

An amphipathic molecule is a molecule that contains both hydrophilic (water-attracting) and hydrophobic (water-repelling) parts. A classic example is a phospholipid, which has a hydrophilic phosphate head and two hydrophobic fatty acid tails. This dual nature allows phospholipids to form bilayers in the plasma membrane.

Describe phospholipid's basic structure in membranes.

A phospholipid consists of a hydrophilic phosphate head and two hydrophobic fatty acid tails. The head is polar and interacts with water, while the tails are nonpolar and repelled by water. This structure is key to forming the phospholipid bilayer of the plasma membrane, where the heads face the aqueous environment, and the tails are oriented inward, away from water.

Explain why phospholipids form bilayers in water.

Phospholipids form bilayers in water due to their amphipathic nature. The hydrophilic heads are attracted to water, while the hydrophobic tails are repelled by water. In an aqueous environment, phospholipids arrange themselves in a bilayer, with the hydrophilic heads facing outward toward the water and the hydrophobic tails tucked inward, away from water. This arrangement minimizes the exposure of the hydrophobic tails to water, creating a stable membrane structure.

Describe the function of integral membrane proteins (IMPs).

Integral membrane proteins (IMPs) are embedded within the phospholipid bilayer and play vital roles in:

1. Transport: IMPs act as channels or carriers to facilitate the movement of substances across the membrane, including ions, nutrients, and waste products.

2. Signal Transduction: IMPs function as receptors for signaling molecules, allowing the cell to respond to external stimuli.

3. Structural Support: IMPs contribute to the structural integrity of the membrane by anchoring the cytoskeleton and linking the membrane to the extracellular matrix.

Describe how water crosses the plasma membrane.

Water crosses the plasma membrane primarily via osmosis, a form of passive transport. Water molecules move through the lipid bilayer, but most notably through aquaporins, which are specialized membrane channels that facilitate the rapid transport of water. This process is driven by osmotic gradients to maintain cellular water balance.

Distinguish between integral proteins, peripheral proteins, and glycoproteins.

• Integral proteins span the membrane, embedded within the lipid bilayer, and are involved in transport, signaling, and structural support.

• Peripheral proteins are associated with the inner or outer surface of the membrane and are not embedded within it. They assist in signaling, maintaining cell shape, and interacting with the cytoskeleton.

• Glycoproteins are proteins with carbohydrate chains attached to them, involved in cell recognition, communication, and immune responses.

Describe cholesterol.

Cholesterol is a lipid molecule found within the phospholipid bilayer of the plasma membrane. It has a rigid, ring-like structure that helps maintain the fluidity of the membrane by preventing the phospholipids from packing too closely together. Cholesterol also plays a role in stabilizing the membrane’s structure across different temperatures.

Discuss how cholesterol affects the fluidity of the plasma membrane

Cholesterol regulates the fluidity of the plasma membrane by:

• At high temperatures, cholesterol stabilizes the membrane by reducing its fluidity, preventing the membrane from becoming too loose.

• At low temperatures, cholesterol prevents the membrane from becoming too rigid, maintaining some flexibility. In both cases, cholesterol ensures that the membrane maintains optimal fluidity for proper cellular function.

Draw a labelled diagram of the plasma membrane

• Phospholipid bilayer: Showing the hydrophilic heads facing outward and the hydrophobic tails facing inward.

• Integral proteins: Spanning the membrane, shown as channel or carrier proteins.

• Peripheral proteins: Attached to the inner or outer surface of the membrane.

• Cholesterol: Embedded in the bilayer for membrane stability.

• Glycoproteins and glycolipids: Present on the outer surface, contributing to cell recognition.

• Aquaporins: Indicating water channels (if relevant).

Define diffusion.

Diffusion is the passive movement of molecules from an area of high concentration to an area of low concentration until equilibrium is reached. It does not require energy (ATP).

Explain the factors that affect diffusion.

The rate of diffusion is affected by:

• Concentration gradient: A steeper gradient increases diffusion speed.

• Temperature: Higher temperatures increase molecular movement, speeding up diffusion.

• Particle size: Smaller molecules diffuse faster than larger ones.

• Medium: Diffusion occurs faster in gases than in liquids or solids due to greater particle movement

Identify an example of diffusion in the human body.

The exchange of gases in the lungs: Oxygen diffuses from the alveoli into the blood, and carbon dioxide diffuses from the blood into the alveoli.

Define osmosis.

Osmosis is the passive movement of water molecules across a semi-permeable membrane, from an area of low solute concentration to an area of high solute concentration, until equilibrium is reached.

Describe the key features of osmosis.

• Water moves from a region of low solute concentration to high solute concentration.

• Occurs across a semi-permeable membrane that allows water but not solutes to pass.

• Passive process that does not require energy.

• Continues until equilibrium is reached.

Predict the Effect of a Hypotonic, Hypertonic, and Isotonic Solution on a Cell

• Hypotonic Solution: Water enters the cell, causing it to swell (may burst in animal cells).

• Hypertonic Solution: Water leaves the cell, causing it to shrink (crenation in animal cells, plasmolysis in plant cells).

• Isotonic Solution: No net movement of water; the cell remains the same size.

Explain the Role of Osmosis in Plant Cells

Osmosis helps maintain turgor pressure in plant cells. In a hypotonic solution, water enters the vacuole, making the cell turgid, which supports plant structure. In a hypertonic solution, water leaves the vacuole, causing the cell to plasmolyze, leading to wilting.

Compare Osmosis and Diffusion

• Molecules Moved:

  • Diffusion: Any molecule (e.g., gases, solutes)

  • Osmosis: Only water molecules

• Membrane Requirement:

  • Diffusion: Can occur with or without a membrane

  • Osmosis: Requires a semi-permeable membrane

• Direction of Movement:

  • Diffusion: Moves from high concentration to low concentration

  • Osmosis: Moves from low solute concentration to high solute concentration

• Energy Requirement:

  • Both are passive processes (do not require energy)

Define semi-permeability.

Semi-permeability refers to the property of the plasma membrane that allows certain molecules to pass through while restricting others, based on size, charge, or solubility.

Explain how semi-permeability maintains balance between the internal and external environments of a cell.

• The plasma membrane regulates what enters and exits the cell to maintain homeostasis.

• Allows small, non-polar molecules (e.g., oxygen, carbon dioxide) to diffuse freely.

• Uses protein channels for larger or charged molecules (e.g., glucose, ions).

• Prevents harmful substances from entering, while facilitating nutrient uptake and waste removal.

• Ensures the cell’s internal environment remains stable despite external fluctuations.

Identify the internal and external environment of a cell.

• The internal environment of a cell refers to the cytoplasm and organelles, where cellular processes occur.

• The external environment consists of the extracellular fluid, which supplies nutrients and removes waste.

• The plasma membrane separates these environments and regulates the exchange of substances.

Define active transport.

Active transport is the movement of molecules or ions across a membrane against their concentration gradient (low to high concentration), requiring ATP and carrier proteins.

Explain how the plasma membrane maintains homeostasis in a cell.

• The semi-permeable membrane regulates the movement of substances in and out of the cell.

• Passive transport (diffusion, osmosis, facilitated diffusion) allows essential molecules (e.g., oxygen, water) to enter without energy expenditure.

• Active transport processes (e.g., ion pumps, endocytosis, exocytosis) move substances against concentration gradients, requiring ATP.

• Prevents entry of harmful substances while ensuring the uptake of nutrients and removal of wastes.

Define homeostasis in relation to the internal and external environment of a cell.

Homeostasis is the maintenance of a stable internal environment within a cell, despite changes in the external environment. It ensures optimal conditions for enzyme activity, cellular function, and survival.

Describe the importance of active transport in cellular function.

• Enables cells to absorb nutrients even when they are in low external concentrations (e.g., root cells absorbing mineral ions from soil).

• Maintains ion gradients necessary for nerve impulses (e.g., sodium-potassium pump in neurons).

• Allows removal of waste products that cannot diffuse passively.

• Ensures a stable internal environment by regulating solute concentrations.

Define endocytosis.

Endocytosis is an active transport process where the plasma membrane engulfs external substances, forming a vesicle to bring them into the cell.

Distinguish between phagocytosis and pinocytosis.

• Phagocytosis (“cell eating”): The cell engulfs large particles (e.g., bacteria, food particles) into a vesicle for digestion.

• Pinocytosis (“cell drinking”): The cell engulfs liquids or dissolved substances into small vesicles.

Define exocytosis.

Exocytosis is an active transport process where a vesicle containing substances fuses with the plasma membrane, releasing its contents out of the cell.

Explain how passive and active transport work together to maintain homeostasis.

• Passive transport (diffusion, osmosis, facilitated diffusion) allows molecules like oxygen, CO₂, and water to move freely, ensuring a stable environment.

• Active transport (ion pumps, endocytosis, exocytosis) moves essential molecules against gradients, preventing deficiencies and imbalances.

• Together, these processes regulate nutrient uptake, waste removal, and cell signaling, maintaining cellular stability.

Compare endocytosis and exocytosis.

Feature	Endocytosis	Exocytosis

Definition

Process of taking substances into the cell via vesicles

Process of releasing substances out of the cell via vesicles

Types

Phagocytosis, Pinocytosis

Secretion of hormones, neurotransmitters

Energy Requirement

Requires ATP

Requires ATP

Effect on Plasma Membrane

Decreases membrane size

Increases membrane size

Explain the role of exocytosis in maintaining cellular function.

• Removes waste materials from the cell.

• Secretes hormones (e.g., insulin from pancreatic cells).

• Releases neurotransmitters from nerve cells for communication.

• Helps renew and modify the plasma membrane by recycling vesicle components.