Bio Ch1 Questions!

Explain the property that allows multicellular organisms to function efficiently [2]

Emergent property
Different parts with different functions interact --> additional property emerges

Both are electron microscopes

not live specimens, black and white only

TEM

thin, 2D

SEM

thick, 3D

Light

max 200nm resolution

Electron

max 0.2nm resolution

Explain why cells differentiate, using examples within your answer [5]

- Every cell with a nucleus contains an organism’s genome
- Only certain genes are expressed during differentiation
- Allows different functions by different cells
- Multicellular organisms are more complex
- Emergent properties arise
- So organism is better adapted/suited to its environment
- E.g. white blood cells, cardiac muscle, epithelial, root hair, guard cell etc

Identify two ways in which striated muscle fibres are different [2]

- Long
- Multinucleated
- No cell wall
- No vacuole
- No chloroplasts

Explain how young tadpoles are able to get enough oxygen to their cells without developed gills [2]

- Diffusion of oxygen
- Short diffusion pathway / large surface area to volume ration

Describe how you would prepare and view a sample of cells from this tissue using a light microscope [5]

- Place single layer of cells on slide
- Add drop of water
- Place slide on microscope stage
- Focus using lowest power lens
- Use larger coarse-focusing knob
- Use fine-focusing knob to sharpen the image
- Increase magnification by using higher power lens
- Only use fine-focusing knob at higher objective powers

List 3 differences between prokaryotic and eukaryotic cells [3]

Prokaryotic cells have 70S ribosomes, circular chromosomes, don’t have nucleus, don't have membrane-bound organelles, aren’t compartmentalised and aren’t associated with proteins

List 4 processes that scientists believe were required for the first cells to be formed [4]

1. Simple organic molecules synthesised from inorganic molecules
2. Simple molecules assemble into polymers
3. Some polymers developed ability to self-replicate
4. Formation of membrane around simple molecules / molecules become isolated from surroundings

Outline the evidence scientists have provided to explain the origin of eukaryotic cells [4]

- Mitochondria and chloroplasts have similar structure to prokaryotes
- Both reproduce by binary fission
- Both have double membranes
- Both have their own 70S ribosomes
- Both have circular, non-membrane bound DNA
- Both transcribe DNA and use mRNA to synthesise their own proteins

Outline the experiment Pasteur used to demonstrate cells only come from pre-existing cells [6]

- Falsified concept of spontaneous generation
- Used culture medium in swan-necked flasks
- Sterilised to kill pre-existing microorganisms
- Didn’t show growth because microorganisms couldn’t enter flask
- Broke neck of flask → showed growth because it was contaminated by air and microorganisms could enter flask

Structures not visible with a light microscope

Mitochondria, ribosome
Endoplasmic reticulum
Lysosome
Cell-surface membrane

TEM vs SEM

Both are electron microscopes: not live specimens, black and white only
TEM: thin, 2D
SEM: thick, 3D

Light vs electron microscopes

Light: max 200nm resolution
Electron: max 0.2nm resolution

Examples of small, non-polar molecules

oxygen, carbon dioxide

How are potassium ions transported across the membrane [2]

It's a charged particle --> facilitated diffusion via channel/carrier protein

How electron micrographs falsified the Davson-Danielli model [2]

1. Freeze-etched electron micrographs showed evidence of proteins extending into centre of membrane
2. Fluorescent markers attached to membrane proteins showed that the proteins in membranes move
3. Biochemical analysis of membranes showed proteins were globular / varied in size --> doesn't form continuous membrane layers
4. Proteins contain hydrophobic regions which would orientate towards the center of the membrane

Functions of membrane proteins [5]

1. cell recognition
2. cell adhesion
3. receptors / binding site for hormones/neurotransmitters
4. transport (e.g. facilitated diffusion, active transport)
5. immobilised enzymes

Describe the Davson-Danielli model [4]

- Protein layers above and below phospholipid layers
- Proteins formed a continuous layer (uniform size and shape)
- Because of the difficulty of movement of substances across the membrane AND electron micrograph images showing 2 darker protein layers
- Falsified by freeze-etched micrographs showing irregular rough surfaces

Describe the Singer-Nicolson model [3]

1. Fluid mosaic model
2. Shown by freeze-fracturing
3. Membranes were fluid
4. Globular proteins were peripheral and integral + dispersed throughout membrane (transmembrane)
5. Proteins could move laterally within the membrane
6. Proteins have diff size and shape
7. Membranes have diff thicknesses and no of protein

Describe the properties that allow some molecules to diffuse rapidly across the cell membrane [2]

small
hydrophobic / water-insoluble / lipid-soluble

How was the electron micrograph in the Davson-Danielli model misinterpreted [2]

- thought it was a single cell membrane (dark lines were 2 protein layers, light region was phospholipid)
- but it is actually the membranes of 2 adjacent cells

Compare and contrast the functions of life in a Paramecium with a named photosynthesising organism [5]

Similarities ("compare"):
- Metabolism: enzyme-controlled metabolic reactions
- Homeostasis: regulated internal environment
- Reproduction: both sexual and asexual reproduction

Differences ("contrast"):
- Growth: paramecium ingests organic matter; chlorella undergoes photosynthesis and absorption
- Response: both react to stimuli, but paramecium reacts to touch; chlorella reacts to light
- Excretion: paramecium expels co2 as waste; chlorella expels o2 as waste
- Nutrition: paramecium ingests and digests; chlorella photosynthesises

Distinguish between the function of free ribosomes and rough endoplasmic reticulum [2]

- Free ribosomes synthesise proteins used within cell
- Ribosomes on rough endoplasmic reticulum synthesise proteins that are released from cell

Spontaneous generation --> cells come from pre-existing cells. Outline the evidence that has allowed this change in universal acceptance [3]

- Pasteur's swan-neck flask experiment
- Ultrastructure of cells can't be synthesised by humans
- Growth is due to mitosis/meiosis
- Viruses with simpler structure can only be produced within host cell
- Genetic code is universal

Describe Miller and Urey's experiment [3]

- Steam/boiling water = early primordial soup
- Mix methane, hydrogen and ammonia = atmosphere
- Electrical discharges = lightning
- Cool mixture = condensation of water in atmosphere
- Analysing the condensed mixture and finding traces of simple organic molecules found

Compare the structure and function of the rough endoplasmic reticulum and golgi apparatus [2]

both involved in protein production
both have cisternae

Explain the Oparin-Haldine hypothesis scientists proposed for the origin of the first cells [5]

- First cells arose from non-living materials
- Simple organic molecules are synthesised from inorganic molecules (Miller and Urey)
- Simple molecules assembled into polymers
- Some of the polymers/mRNA developed ability to self-replicate
- Formation of membranes surrounding the polymers created packages with internal chemistry diff from surroundings

Discuss the theory that suggests how an organism could have evolved to be an eukaryotic cell that is both heterotrophic and autotrophic [7]

Endosymbiotic theory
- Eukaryotes evolved from prokaryotes
- A larger prokaryote engulfed by endocytosis of a smaller prokaryote
- Mitochondria and chloroplasts were thought to have evolved from these smaller prokaryotes bc they display characteristics of prokaryotic cells
- But the theory doesn't explain the origins of certain structures (e.g. cilia and flagella) or processes (e.g. meiosis)
- The theory can't be falsified as it occurred in the past

Examples: mitochondria/chloroplasts
- Both reproduce by binary fission
- Both contain their own circular, non-membrane bound DNA
- Both have 70S ribosomes
- Both transcribe DNA and use mRNA to synthesis their own proteins
- Both have double membranes

Explain how the difference in sodium concentration between RBC and blood plasma is maintained

Active transport by sodium-potassium pump, requires ATP

Explain how proteins would be transported from mother's blood to fetus

Endocytosis/phagocytosis
Formation of vesicles

Describe how the structure of the membrane allows for the transport of proteins from the mother to the fetus

- Fluidity of membrane allows shape change / formation of vesicles
- Active process, requires ATP and proteins
- Phospholipid bilayer enables the membrane to be fluid
- Cholesterol / kinks in phospholipid tails affect the fluidity of the membrane

Why use percentage in mass rather than the change in actual mass? [2]

- For comparison, as initial masses aren't same
- Gives idea of proportional change from original mass / better measure of relative change