B2.1 Flashcards
What is diffusion?
Net movement of particles from high to low concentration.
Is diffusion passive or active?
Passive – no energy required.
Which small molecules move by diffusion?
Oxygen, glucose, amino acids, water.
Can large molecules like starch diffuse?
No – too big to pass through membranes.
Why can single-celled organisms rely on diffusion?
Large surface area to volume ratio; low metabolic demand.
Why can’t multicellular organisms rely on diffusion alone?
Small surface area to volume ratio; need specialised systems.
Examples of adapted exchange surfaces in multicellular organisms?
Alveoli (lungs), villi (small intestine), root hair cells (plants).
How does concentration gradient affect diffusion rate?
Greater gradient = faster diffusion.
How does temperature affect diffusion rate?
Higher temperature - more kinetic energy = faster diffusion.
How does surface area affect diffusion rate?
Larger surface area - more room for diffusion = faster diffusion.
What is osmosis?
Movement of water from dilute to concentrated solution through a partially permeable membrane.
Is osmosis passive or active?
Passive – no energy required.
What is a dilute solution in terms of water potential?
High water potential.
What is a concentrated solution in terms of water potential?
Low water potential.
What happens when external and internal solutions are equal?
No net movement – isotonic.
What happens if external solution is more concentrated?
Water moves out – hypertonic.
What happens if external solution is more dilute?
Water moves in – hypotonic.
Effect of hypotonic solution on animal cells?
Water enters; cell may burst.
Effect of hypertonic solution on animal cells?
Water leaves; cell shrivels.
Effect of hypotonic solution on plant cells?
Water enters; cell becomes turgid.
Effect of hypertonic solution on plant cells?
Water leaves; cell becomes plasmolysed.
What is active transport?
Movement of particles from low to high concentration using energy.
Is active transport passive or active?
Active – requires energy from respiration.
Example of active transport in plants?
Root hair cells absorbing mineral ions from soil.
Why is active transport needed in root hair cells?
Mineral ions often more concentrated in cells than soil.
Example of active transport in animals?
Absorption of glucose and amino acids in the gut.
Why is active transport needed in the gut?
Sometimes lower concentration of sugar molecules in the gut than in the blood.
What is mitosis?
Cell division to produce 2 identical daughter cells.
What is mitosis used for?
Growth, repair, and devolpment.
What must happen to chromosomes before mitosis?
DNA must be replicated.
What does each chromosome form after replication?
Two chromatids joined by a centromere.
What are the three stages of the cell cycle?
Interphase, mitosis, cytokinesis.
What happens during interphase?
Cell grows, organelles increase, proteins made, chromosomes replicate.
What happens during mitosis?
Chromosomes line up and chromatids are pulled apart to opposite sides. - spindle fibres
What happens during cytokinesis?
Cytoplasm divides, forming two identical cells.
How many chromosomes do daughter cells have?
46 – same as parent cell.
Are the daughter cells genetically different?
No – they are identical.
Why is genetic identity in mitosis important?
Ensures same function/structure in new cells.
What is cell differentiation?
When a cell changes to become specialised.
What happens during differentiation?
Cell gains sub-cellular structures to carry out specific roles.
When do animal cells usually differentiate?
At an early stage.
Can adult animal cells differentiate?
Most can’t – only used for repair/replacement.
Do plant cells retain the ability to differentiate?
Yes – many differentiate throughout life.
How is a sperm cell adapted?
Long tail - flagella, streamlined, many mitochondria - supply energy due to respiration, acrosome (enzymes break the egg outer layers)
How is a nerve cell adapted?
Long axon- carried long distances, dendrites - branched connections to other cells, synapses with neurotransmitters - impulse from one cell to another
How is a muscle cell adapted?
Proteins (myosin & actin) that slide - muscle can contract , mitochondria - energy due to respiration , glycogen stores - used for respiration.
How is a root hair cell adapted?
Big surface area - more water can move in, vacuole for osmosis, mitochondria (provide energy) for active transport.
How is a xylem cell adapted?
Lignin strengthens, cells die to form hollow tubes.
How is a phloem cell adapted?
Sieve plates allow flow, companion cells give energy.
What is a stem cell?
An undifferentiated cell that can divide to produce more similar cells.
What can stem cells differentiate into?
Different specialised cells.
What are stem cells important for?
Development, growth, and repair.
What are the 3 types of stem cells in the spec?
Embryonic, adult, and meristem (plants).
How are embryonic stem cells formed?
When a sperm and egg fuse to form a zygote.
What can embryonic stem cells become?
Any type of cell in the body.
How are embryonic stem cells cloned?
By culturing in labs and directing them to differentiate.
Give 3 medical uses for embryonic stem cells.
Replace insulin-producing cells (diabetes)
New neural cells (Alzheimer’s)
Nerve cells (spinal injuries)
Where are adult stem cells found?
Bone marrow.
What can adult stem cells become?
Many types of cells, e.g. blood cells (but not all types like embryonic).
Where are meristem cells found?
Where are meristem cells found?
What can meristem cells become?
Any type of plant cell.
Do meristem cells stay active throughout life?
Yes
What are 3 reasons meristem cells are used in cloning plants?
Desirable features (e.g. disease resistance)
Research
Saving rare species from extinction
