Bio Bio 2

Second bio test, covering the material from the second section of the first unit:

What property of phospholipids allows them to form bilayers in water?

They are amphipathic — having hydrophilic heads and hydrophobic tails, which naturally form sheet-like bilayers in water.

Why do lipid bilayers act as effective barriers?

The hydrophobic core formed by hydrocarbon chains has low permeability to large molecules and hydrophilic particles (including ions and polar molecules), preventing them from crossing easily.

What are glycoproteins and glycolipids in membranes and what are their roles?

They are carbohydrates attached to proteins or lipids on the extracellular side of membranes. Their roles include cell adhesion and cell recognition.

What does the fluid mosaic model show?

A membrane with a phospholipid bilayer containing integral & peripheral proteins, glycoproteins, and cholesterol, showing hydrophilic and hydrophobic regions.

How do unsaturated fatty acids affect membrane fluidity? (HL)

Unsaturated fatty acids have lower melting points, making membranes more fluid and flexible at normal temperatures.

How do saturated fatty acids affect membrane structure? (HL)

They have higher melting points, making the membrane stronger and less fluid at higher temperatures.

What is the role of cholesterol in animal cell membranes? (HL)

Cholesterol modulates membrane fluidity — stabilizes membranes at high temperatures and prevents stiffening at low temperatures.

How is membrane fluidity related to vesicle formation? (HL)

Fluid membranes allow endocytosis (vesicle entering the cell) and exocytosis (vesicle exiting the cell).

What is simple diffusion across membranes?

Passive movement of small nonpolar molecules like oxygen and carbon dioxide between phospholipids, down their concentration gradient.

What is the difference between integral and peripheral membrane proteins?

Integral proteins are embedded in one or both layers of the membrane; peripheral proteins are attached to its surface.

What is osmosis and what role do aquaporins play?

Osmosis is the passive movement of water across membranes. Aquaporins are channel proteins that speed up water transport.

How do channel proteins enable facilitated diffusion?

They allow specific ions to pass through only when the channels are open, making membranes selectively permeable.

How do pump proteins achieve active transport?

They use energy from ATP to move specific particles across membranes against their concentration gradient.

What makes membrane permeability selective?

Facilitated diffusion and active transport are selective; simple diffusion depends only on size and polarity of particles.

What allows solutes to dissolve in water?

Formation of hydrogen bonds and attraction between water molecules and ions/polar molecules.

From which solution does water move during osmosis?

From less concentrated (hypotonic) to more concentrated (hypertonic) solutions.

What do hypertonic, hypotonic, and isotonic mean?

• Hypotonic: lower solute concentration

• Hypertonic: higher solute concentration

• Isotonic: equal solute concentration, dynamic equilibrium

What happens to plant tissue in hypotonic vs hypertonic solutions?

• Hypotonic: turgor pressure develops

• Hypertonic: plasmolysis occurs
  Students may measure length/mass change and analyze data using standard deviation/error.

What are medical uses of isotonic solutions?

Used in IV fluids and bathing organs before transplantation.

What is water potential? (HL)

The potential energy of water per unit volume, measured relative to pure water at 20°C and atmospheric pressure (units: kPa).

Which direction does water move in terms of water potential? (HL)

From higher water potential to lower water potential.

What contributes to water potential in cells with walls? (HL)

Solute potential + pressure potential.

What is cytokinesis?

Splitting of cytoplasm:

What is unequal cytokinesis? Give examples.

Uneven division of cytoplasm; examples include oogenesis in humans and budding in yeast.

What are the phases of mitosis?

Prophase → Metaphase → Anaphase → Telophase (producing 2 genetically identical daughter cells).

What is cell proliferation and when does it occur? (HL)

Rapid cell division for growth and tissue repair — e.g., plant meristems, embryos, and skin renewal/healing.

What is the cell cycle? (HL)

A sequence: Interphase (G1, S, G2) → Mitosis → Cytokinesis.

What happens during interphase?

Active growth and biosynthesis of proteins & DNA; mitochondria/chloroplasts increase by dividing.

How is the cell cycle controlled? (HL)

Using cyclins, which rise and fall in concentration. Each checkpoint needs a threshold cyclin level to pass.

What happens if genes controlling the cell cycle mutate? (HL)

Proto-oncogenes may become oncogenes; tumour suppressor genes may fail → uncontrolled cell division.

What are stem cells?

Cells that can divide endlessly and differentiate into various types.

What are stem cell niches? Give examples.

Regions that maintain or activate stem cells. Examples: bone marrow & hair follicles.

What are totipotent, pluripotent, and multipotent stem cells?

• Totipotent: can form all cell types (early embryos)

• Pluripotent: can form many types

• Multipotent: limited types (e.g., adult bone marrow)

How does cell size relate to specialization?

Cells vary in size depending on function — e.g., gametes, blood cells, neurons, muscle fibers.