2 - Foundations in Biology

What is a light microscope used for?

Observing living and dead specimins

What are the pros and cons of a light microscope?

Pros: Cheap, portable, easy to use, can study living specimens. Cons: Limited magnification, poor resolution.

What is a laser scanning confocal microscope used for?

Creating a high resolution, high contrast image, at different depths of the specimen.

What is a transmission electron microscope be used for?

Observing the internal ultrastructure of cells under high magnification and resolution

What is a scanning electron microscope used for?

Viewing the surface of objets under high magnification and resolution

What are the pros and cons of an electron microscope?

Pros: Very high magnification and excellent resolution. Cons: specimen has to be dead, very expensive, very large, needs great skill and training to use.

What is the difference between a transmission and an scanning electron microscope?

TEM sends a beam of electrons through the specimen, the SEM bounces electrons off the surface.

What is the difference between light and electron microscopes?

Light uses lenses to focus a beam of light. Electron uses a beam of electrons, focused by magnets.

What is an eye piece graticule?

A small ruler fitted to a light microscope's eyepiece. It must be calibrated using a stage micrometer before being used to measure specimens.

What is a stage micrometer?

A millimeter long ruler etched onto a slide. it has 100 divisions, each of 0.01mm or 10 micrometers. It is used to calibrate the eyepiece graticule

Why do we stain specimens?

To provide more contrast, and make it easier to distinguish certain parts.

What is differential staining?

Using a stain to distinguish between either 2 different orgaisms, or between organelles of a specimin due to preferential absorbtion of stain.

What is the formula to calculate magnification?

Magnification = Image size / Actual size

What is the formula to calculate actual object size?

Actual size = Image size / Magnification

How do we work out image size?

Use a ruler and measure the image.

What is magnification?

A measure of how much larger the image of a specimen looks under the microscope

What is resolution?

The ability to distinguish between to adjacent individual points as separate.

What are the maximum resolutions of the different microscopes?

Light: 200nm; SEM: 10nm; TEM: 0.2nm.

What is the maximum magnification of the different microscopes?

Light: 1,500X; SEM: 100,000X; TEM: 500,000X.

What are the main structures of all eukaryotic cells?

Nucleus; nucleolus; cytoplasm; cytoskeleton; plasma membrane;mitochondria; Golgi apparatus; smooth endoplasmic reticulum; rough endoplasmic reticulum; ribosomes.

What is the structure and function of the nucleus?

Surrounded by a double membrane (the nuclear envelope). Contains chromatin (DNA wound around histones). Stores the human genome, controls the cell by providing instructions for protein synthesis.

What is the structure and function of the nucleolus?

Made of RNA, produces ribosomes.

What is the structure and function of the nuclear envelope?

A double membrane embeded with channel proteins forming pores. Separates the nucleus from the rest of the cell. Pores allow ribosomes and mRNA to leave the nucleus.

What is the structure and function of the rough endoplasmic reticulum (RER)?

A system of fluid filled membranes studded with ribosomes. Continuous with the nuclear membrane. Large surface area formed by folding, enables lots of protein synthesis. Proteins pinched off in vesicles transported to the Golgi apparatus.

What is the structure and function of the smooth endoplasmic reticulum (SER)?

A system of fluid filled membranes. No ribosomes. Contain enzymes for cholesterol, lipid and phospholipid synthesis.

What is the structure and function of the Golgi apparatus?

A stack of flattened membrane bound sacs. Vesicles from the RER join at the cis face. Here they are modified, by adding sugar to make glycoproteins, adding lipids to form glycolipids. Folding proteins into their 3D shape. Modified proteins are pinched off from the trans face into transport vesicles.

What is the structure and function of the ribosomes?

2 subunits, large and small. Made of rRNA . Proteins synthesised here.

What is the structure and function of the mitochondria?

Double membrane bound. Inner membrane folded into cristae within a fluid filled matrix. Contain own DNA and 70s ribosomes. Site of aerobic respiration.

What is the structure and function of the lysosomes?

Membrane bound sacs containing hydrolytic (digestive) enzymes. break down old organelles and foreign matter for reuse.

What is the structure and function of the chloroplasts?

Double membrane bound. Inner membrane forms flat discs filled with chlorophyll called thylakoids, in stacks called granum. These are surrounded by a fluid matrix called the stroma. Contain own DNA and 70s ribosomes. Site of photosynthesis.

What is the structure and function of the plasma membrane?

Phospholipid bilayer, cholesterol, proteins, glycoproteins, glycolipids. Separates cell contents from external environment. Controls what enters and leaves the cell. Identifies cell as self. Acts as a receptor for various chemicals. site of chemical reactions.

What is the structure and function of the centrioles?

Present in animals only. Two bundles of microtubules at right angles. Used as an anchor point to separate chromosomes during cell division. Form the basis of cilia.

What is the structure and function of the cell wall?

Present in plants and fungi only. Bundles of cellulose fibres in plants. Chitin in fungi. Provides support and strength, maintaining the cell's shape. prevents the cell from bursting when turgid. Permeable to allow solutions through.

What is the structure and function of the flagella?

9 pairs of microtubules surround 2 lone microtubules. A membrane covers the whole thing. Used for moving unicellular organisms around.

What is the structure and function of the cillia?

9 pairs of microtubules surround 2 lone microtubules. A membrane covers the whole thing. Present in great numbers. Move together in a wafting pattern to move single celled organisms. When present on tissues waft to move fluids such as mucus.

Which structures are involved in the production of proteins?

Nucleus; RER; transport vesicle; Golgi apparatus

What is the structure and function of the cytoskeleton?

Microfilaments made of actin - allow cell movement and cytokinesis. Microtubules made of tubulinsscaffold like structures to give cell shape. Intermediate fibres give mechanical strength, maintaining integrity.

What do prokaryotic and eukaryotic cells have in common?

Plasma membrane; cytoplasm; ribosomes; DNa and RNA

What is different between prokaryotic and eukaryotic cells?

Prokaryotes have no: Nucleus; centrioles; membrane bound organelles (mitochondria, chloroplast, RER, SER, Golgi apparatus). Prokaryotes also have: peptidoglycan cell wall; smaller ribosomes; naked loop of DNA; plasmids.

How do prokaryotes divide?

Binary fission

List out the elements that make up proteins.

C, H, O, N, S

Explain the polar nature of water.

- O is more electronegative than H / unequal share of e- / e- spend more time orbiting around O than H
- give regions of slight positive and negative

What allows water molecules to have cohesive and adhesive properties?

Hydrogen bond

Describe the structure of amylose, including the bonds involved and the shape.

All 1,4-glycosidic bonds, straight helix

Describe the structure of amylopectin, including the bonds involved and the shape.

1,4 and 1,6 glycosidic bonds, branched

State the two structures that make up starch.

Amylose + Amylopectin

State the reaction that breaks down maltose.

Hydrolysis

What is the reaction to join monosaccharides together?

Condensation

What are the 3 types of polysaccharides that α-glucose can form?

- Amylose
- Amylopectin
- Glycogen

What are the two monosaccharides that join up to make sucrose?

Glucose
+ Fructose

1,6 glycosidic bonds are found on ........

Amylopectin
/ Glycogen

β-glucose can only be found in ........

Cellulose

How are the monosaccharides in cellulose arranged?

Alternative β-glucose molecules are turned upside down

Based on the arrangement of cellulose molecules, explain why cell walls provide strength and support to plant cells.

- cellulose molecules form hydrogen bonds with each other to make microfibrils
- microfibrils join to make macrofibrils
- macrofibrils join to make fibres
- fibres are insoluble and tough

What does the Benedict's test test for?

Reducing sugar

Explain how a positive result is formed in Benedict's test.

Reducing sugar reacts with blue Cu2+
--> to make brick-red Cu+

How can we test for starch?

Iodine solution

How can we use a colorimeter to do a quantitative Benedict's test?

- Colorimeter measure the absorbance or transmission of light by a coloured solution
- More concentrated solution à more light absorbed / less light transmitted
- Compare to data table (known concentrations vs. abs/trans value)

What are the two parts that make up a carboxylic acid?

Carboxyl group + Hydrocarbon chain

How many water molecule(s) is/are needed when breaking down a triglyceride?

3

What is another term for the condensation reaction that makes lipids?

Esterification

What is the difference in structure between saturated and unsaturated lipids?

- Saturated: all single C-C bonds in fatty acid chain
- Unsaturated: 1 or more double C=C bonds in fatty acid chain

Why do oils contain unsaturated triglycerides rather than saturated?

- Unsaturated fatty acids cause the molecule to kink/bend
- cannot pack closely together (ie. Cannot form more H bonds)

What is the difference in structure between triglyceride and phospholipid?

- phospholipid: 2 fatty acid chains + 1 phosphate group
- Triglyceride: 3 fatty acid chains

Describe the phospholipid bilayer arrangement.

- Hydrophilic heads point outwards
- Hydrophobic tails point inwards (shielded from aqueous environment)

Describe 2 similarities and 1 difference between phospholipids and sterols.

- Similarities: both have dual hydrophilic/hydrophobic characteristics / both make up the plasma membrane
- Difference: sterols are complex alcohol molecules; phospholipids are lipids

Describe the steps in identifying lipids and state the positive result.

- mix sample with ethanol
- mix solution with water and shake
- white emulsion layer formed à lipid present

State the monomer of a protein.

amino acids

What are the components that make up an amino acid?

Central carbon + H atom + Amine group + Carboxyl group

Name the bond formed between two amino acids.

Peptide bond

What is the primary structure of a protein?

Amino acid sequence

What is the secondary structure of a protein?

alpha-helix + beta-pleated sheets

What is the tertiary structure of a protein?

Folding into a 3D shape

What is the quaternary structure of a protein?

Binding with other subunits

State the bond involved in the primary structure of a protein.

peptide bond

Stat the bond involved in the secondary structure of a protein

hydrogen bond

State the bond involved in the tertiary structure of a protein.

ionic, covalent, hydrogen, hydrophobic interactions, disulphide bridges

State the bond involved in the quaternary structure of a protein.

ionic, covalent, hydrogen, hydrophobic interactions, disulphide bridges

Name the reaction that breaks down proteins.

hydrolysis

What is the solution used to test for the presence of proteins?

Biuret solution

Describe a positive result for proteins.

Using Biuret solution: Blue to purple

What is thin layer chromatography?

a technique to separate individual components of a mixture (eg. Amino acids)

Based on what principles are the amino acids separated in TLC?

- depends on interactions (H bonds) aa form with silica in the stationary phase
- depends on solubility in the mobile phase

Why should the chromatography plate be only handled by the edges?

prevent contamination with proteins on hands

What are the three types of proteins?

Globular, conjugated, fibrous

Explain why insulin is soluble in blood.

Hydrophilic amino acids are folded on the protein surface

What are prosthetic groups?

non-protein component in a conjugated protein

Give an example of a conjugated protein.

Haemoglobin/Catalase

Compare the haem groups in haemoglobin and catalase.

- Hb: Fe2+ bond reversibly with O2 in blood
- Catalase: Fe2+ allows catalase to interact with H2O2 to speed up its breakdown

How many haem groups do a haemoglobin contain?

4

Explain why keratin is relatively strong, inflexible and insoluble.

Many strong disulfide bridges

Briefly describe the structure of collagen.

3 polypeptides wound together in a long, strong rope-like structure

What bonds do DNA/RNA polymerase catalyse?

Phosphodiester bonds

Name the monomer of a nucleic acid.

Nucleotide

State the five possible bases of a nucleotide.

Adenine, guanine, thymine, cytosine, uracil

State the three components to a DNA nucleotide.

Deoxyribose + Nitrogenous base + Phosphate group

The two strands of the double helix are ............. to each other.

antiparallel

Thymine, cytosine and uracil belong to a group of bases. Name the group.

Pyrimidines

Adenine and guanine belong to a group of bases. Name the group.

Purines

State the complementary base pairings.

A-T/U, C-G

State the number of hydrogen bonds formed between adenine and thymine/uracil.

2

State the number of hydrogen bonds formed between cytosine and guanine.

3

Why is DNA replication described as semi-conservative?

Each new DNA molecule is made up of one new and one old/template strand

State the enzymes involved in DNA replication.

DNA helicase + DNA polymerase

State the function of DNA polymerase.

Catalyses formation of phosphodiester bonds between DNA nucleotides

State the function of DNA helicase.

Unzips DNA double helix, breaking hydrogen bonds

The free nucleotides pair up with the exposed bases on the DNA strands based on ...... (which principle?)

Complementary base pairing

DNA polymerase can only build phosphodiester bonds on the daughter strand in a particular direction. What is this direction?

5' to 3'

In which direction of the template strand does the DNA polymerase move in?

3' to 5'

Define 'genetic code'.

The sequence of bases in DNA that codes for the sequence of amino acids in protein production

The genetic code is described as 'degenerate'. What does that mean?

Many different triplet codes/codons can code for the same amino acid

Define 'gene'.

A section of DNA containing the base sequence that codes for a protein

What is a codon?

Triplet bases on RNA
that codes for an amino acid

What are the two differences between DNA and RNA?

- DNA has deoxyribose; RNA has ribose
- DNA has thymine; RNA has uracil

Name the enzymes involved in transcription.

DNA helicase + RNA polymerase

Why is the antisense strand needed even though it does not code for proteins?

- it acts as the template strand
- to form the complementary mRNA with the same base sequence as the sense strand

What type of bond does mRNA have?

phosphodiester bonds

Even though DNA codes for proteins directly, why is mRNA needed to be made for making proteins?

DNA is too large to leave the nucleus through the nuclear pores

How is rRNA involved in catalysing translation?

- peptidyl transferase is an rRNA component
- it transfers one amino acid to another

Which part of tRNA binds to the mRNA?

anticodon loop

Name the amino acid that is always at the start of a protein.

Methionine

Describe what happens to the amino acid chain to make it a fully functional protein.

- The amino acid chain folds into secondary and tertiary structures
- May undergo further modifications at Golgi

State the two stages of protein synthesis.

Transcription + Translation

Name the product of transcription.

mRNA

Name the product of translation.

Polypeptide (then becomes functional protein after modification in Golgi)

State the location where translation occurs.

Ribosomes

What are the three main types of activities in cells that require energy?

Synthesis, transport, movement

What does 'ATP' stand for and what is it?

Adenosine triphosphate, energy currency

Draw the structure of ATP.

Ribose sugar (pentose with O on top) + adenine on C1 + 3 phosphate groups on C5 (must show C5 as an angle off the pentose sugar)

How does ATP release energy?

ATP is hydrolysed into ADP + Pi, releasing energy

State 3 properties of ATP.

Small - easy to move into and out of cells; Water-soluble; Releases energy in small quantities - so no heat loss; Easily regenerated by phosphorylation of ADP

What are metabolic reactions?

the sum of all reactions in the organism

What are anabolic reactions?

Building up larger molecules

What are catabolic reactions?

Breaking down molecules

What are enzymes?

Biological catalysts that speed up chemical reactions

Name the energy that is required to start a reaction.

Activation energy

What are enzymes' effect on the activation energy of a reaction?

Enzymes lower Ea

Name the area on the enzyme that binds to and reacts with the substrate.

Active site

The active site has a _____ shape to the substrate.

Complementary/Specific

Name the two models used to illustrate enzyme actions.

Lock-and-key + Induced fit

Name the structure where the enzyme and substrate are bound together.

Enzyme-substrate complex

What is the difference between the lock-and-key model and the induced fit model?

Lock-and-key: rigid, no movement; Induced fit: slight movement of active site to allow better binding to substrate

Name an intracellular enzyme.

Catalase

Name an extracellular enzyme.

Amylase/trypsin

Define the term ‘denaturation’.

Loss of active site shape

Explain how an increase of temperature increases enzyme activity.

- Increasing temperature increases particles’ kinetic energy
- Particles move faster and collide more often
- More successful collisions (between active site and substrate)

Explain how high temperatures can denature enzymes.

- High temperature leads to more vibrations
- Too much vibration breaks the bonds that hold the protein together

What is the temperature coefficient (Q10)?

A measure of how much the reaction rate increases with a 10oC increase

How are the enzymes in organisms that live in cold environments adapted?

- enzymes are more flexible, hence less stable
- can move more in low KE environment to bind

How are the enzymes in organisms that live in hot environments adapted?

- enzymes are more stable (have more bonds in tertiary structure)
- more resistant to denaturation by high heat

How does a change in pH affect enzyme structure?

- A change in pH refers to a change in H+ concentration
- H+ ions interact with polar and charged R groups in tertiary structures
- This breaks the bonds/interactions between R groups, leading to loss of tertiary structure

Explain why an increase in substrate concentration increases rate of reaction.

- Higher successful collision rate
- Between active site and the substrate
- Forming more enzyme-substrate complexes

What does it mean by a ‘reversible’ inhibitor?

The inhibitor can be released from the enzyme to resume the enzymes’ function

Most competitive inhibitors are reversible or irreversible?

Reversible

Explain how Vmax of the enzyme can be unchanged in competitive inhibition.

- By adding more substrates to outcompete inhibitors
- More substrates leads to more successful collisions between enzymes and substrates, hence more ESC formed
- Therefore less enzymes available for inhibitors to bind

What types of inhibitor does aspirin belong to?

Irreversible, competitive

Explain the difference between competitive and non-competitive inhibition mechanisms.

- Competitive: inhibitor binds to active site à substrate can no longer bind to AS
- Non-competitive: inhibitor binds to a location other than the active site (allosteric site) à changes 3o structure, hence change AS shape

Explain how an increase in substrate concentration affects the rate of reaction in non-competitive inhibition.

No change
, as active site is altered by inhibitor binding in allosteric side

State two examples of irreversible, non-competitive inhibitors for human use.

- Organophosphates à insecticides and herbicides (inhibits AChE)
- Proton pump inhibitors (PPIs) à treat long term indigestion

What is end-product inhibition?

The product of an enzyme-catalysed reaction acts as the inhibitor

How does ATP regulate its own production by end-product inhibition?

- ATP binds to the allosteric site of PFK
- Prevent second phosphorylation of glucose
- Glucose is not broken down to produce more ATP

State the difference between cofactors and coenzymes.

- Cofactors = a non-protein component to help enzymes carry out their functions
- Coenzymes = organic cofactors

From which chemical are cofactors derived from?

Minerals

From which chemical are coenzymes derived from?

Vitamins

Name the cofactor found in amylase.

Chloride ion

Name the cofactor invovled in photosynthesis.

NADP

Name the cofactor invovled in respiration.

NAD + FAD

State the difference between cofactors and prosthetic groups.

- Cofactors are temporarily bound to the enzyme
- Prosthetic groups are permanently bound

Name the prosthetic group in haemoglobin.

Iron ion in haem group

Name the prosthetic group in carbonic anhydrase.

Zn2+

What are the three ways that an enzyme can be activated by changing the tertiary structure?

- Adding a cofactor
- action of another enzyme (eg. Cleaving bonds to activate enzyme)
- Change in condition (eg. pH)

Why is it important that some enzymes are produced in its inactive form?

Otherwise it may damage the cell it was produced in

What is an apoenzyme?

Inactive form of enzyme

What is a holoenzyme?

Active form of enzyme

What is the fluid mosaic model?

The theory of the cell membrane formed from a sea of phospholipids emmeded with proteins.

What is a glycolipid?

A lipid with a carbohydrate molecule attached.

What is a glycoprotein?

A protein with a carbohydrate molecule attached.

State four functions of membranes at the surface of cells

Compartmentalisation (separates cell's components from its external surroundings ensuring conditions inside cell remain unaffected); regulates transport of material into and out of cells (endocytosis and exocytosis); has surface antigens so the body's immune system recognises the cell as 'self'; contains receptors for chemical signals (hormones, drugs etc); may be the site of chemical reactions

State 3 functions of membranes within cells

Compartmentalisation (maintains specific conditions for metabolic reactions to take place, e.g. photosynthesis in chloroplasts, aerobic respiration in mitochondria); inner mitochondrial membrane is highly folded providing a larger surface area for electron carrier proteins; thylakoid membranes within chloroplasts house chlorophyll, the primary pigment required for light absorption in photosynthesis; vesicle production.

The principal design of the plasma membrane consists of two layers; what name is given to these two layers?

Phospholipid bilayer

Explain the orientation of phospholipids within the bilayer

Hydrophilic phosphate heads are orientated outwards (towards water); hydrophobic fatty acid tails are orientated inwards (away from water)

Describe the function of glycoproteins and glycolipids in the phospholipid bilayer

As markers or antigens; cell signalling; cell communication; call adhesion

Give 3 examples of intrinsic proteins

Channel proteins, carrier proteins, glycoproteins

Channel proteins and carrier proteins have what main role within the membrane?

Transport

Describe the position and role of cholesterol in the membrane

Interspersed between phospholipid molecules; regulates fluidity of membrane by coming between phospholipids preventing crystallisation. Also bonds to phospholipids, preventing it becoming too fluid.

Describe the structure of a phospholipid

Glycerol backbone; one hydrophilic phosphate head; two hydrophobic fatty acid tails

Describe the effects of temperature on membrane structure

As temperature increases, phospholipids will have more KE, so move faster and more, making the bilayer more fluid and it begins to lose its structure. This loss of structure allows molecules to cross it more easily. Carrier and channel proteins may become denatured, affecting membrane transport.

Describe the effects of ethanol on membrane structure

Non-polar ethanol molecules can insert themselves into the bilayer (hydrophobic tails) disrupting the structure, meaning the bilayer becomes more fluid and permeable

Explain why alcohol is used in antiseptic wipes.

Alcohol can disrupt and dissolve bacteria's membrane due to their non-polar nature, killing them

Define the term diffusion.

The net movement of a substance from an area of high concentration to an area of low concentration. It is passive, does NOT require ATP.

Define the term facilitated diffusion

Movement of molecules from a high concentration to a low concentration, across a partially permeable membrane, via specific channel or carrier proteins. It is passive, does NOT require ATP

What is a channel protein?

A protein which creates a fluid filled pore in the cell membrane through which ions and small polar molecules can pass.

What is a carrier protein?

A protein which changes shape to allow larger molecules to pass through the membrane. In facilitated diffusion this requires no energy, in active transport it requires ATP.

What types of molecules can diffuse directly across the phospholipid bilayer?

Small molecules such as oxygen and carbon dioxide; lipid-soluble molecules such as steroid hormones and alcohol

Describe the movement of water across the phospholipid bilayer

Water is polar and insoluble in lipid, BUT because it is present in such high quantities, significant direct, simple diffusion does occur. In membranes (e.g. collecting duct) where a very high rate of water movement is required, special channel proteins known as aquaporins are inserted into the membrane.

State 5 factors that affect the rate of simple diffusion

Temperature, surface area, diffusion distance, size of molecule, concentration gradient

Define the term active transport

Movement of molecules, against their concentration gradient (using energy liberated from ATP hydrolysis) using specific protein channels or carriers

Describe how carrier proteins are used in active transport

Molecule binds to specific site in carrier protein; ATP binds to separate binding site; carrier protein changes shape (conformational change) and transports molecule across membrane

Define bulk transport and give two examples

The movement of large molecules that are too big to pass across the plasma membrane. Endocytosis (phagocytosis or pinocytosis) brings large molecules INTO the cell, enclosed in a vesicle. Exocytosis transports large molecules OUT of cells.

Define and describe phagocytosis

The intake of solid particles into the cell by engulfing. Pseudopodia surround the particles, the membrane fuses together, to form a vesicle.

Define and describe pinocytosis

The intake of liquids into the cell by engulfing. The plasma membrane invaginates, and the membrane fuses around the substance, forming a vesicle.

Define and describe exocytosis

The bulk transport of particles too large to pass through the membrane, out of the cell. It works like a reversal of pinocytosis. A vesicle containing the substance fuses with the plasma membrane. The fused site opens, releasing the contents of the secretory vesicle.

Describe the role of ATP in bulk transport

ATP is required to provide energy for the movement of vesicles along microtubules of cytoskeleton (via motor proteins); ATP is needed to fuse vesicle membrane and plasma membrane together (PM is changing shape)

What is the main difference between active transport and facilitated diffusion?

Active transport requires ATP; facillitated diffusion is passive

Define the term osmosis

The movement of water molecules from a region of higher water potential to a region of lower water potential, across a partially permeable membrane

What is water potential?

The tendancy of water molecules to move from one region to another.

What substance has the highest possible water potential of 0 kPa?

Pure water

State the equation that links water potential, solute potential and pressure potential

WP = SP + PP

As more solute is added to a solution, what happens to the solute potential and hence the water potential?

Solute potential decreases, hence water potential decreases

Describe what would happen to a red blood cell placed in a solution with a more negative water potential than that of its cytoplasm

Water would move OUT, down a WP gradient, shrinking to crenation

Describe what would happen to a liver cell placed in a solution with a more positive WP than its own cytoplasm

Water would move IN, down a WP gradient, swelling the cell and causing it to burst (CYTOLYSIS) due to the presence of no cell wall

Describe what would happen to a root hair cell placed in a solution with lower WP than its own cytoplasm/vacuole

Water would move OUT, down a WP gradient, causing the cell to become flaccid and then plasmolysed

Describe what would happen to a guard cell placed in a solution of less negative WP than its own cytoplasm

Water would move IN, down a WP gradient, causing the cell to swell and become TURGID

State three events that occur in G1 phase of the cell cycle

Cells grow and increase in size; proteins from which organelles are made are synthesised (transcribed and translated); organelles replicate

What happens during the S phase of the cell cycle?

This is the synthesis phase, DNA is replicated.

What happens during the G2 phase?

Second growth phase, proteins which involved in making the chromosomes condense are synthesised (transcribed and translated).

Describe what may happen in G0 phase of the cell cycle

Cells may undergo apoptosis, differentiation or senescence

State three cell cycle checkpoints and briefly describe what is being checked for at each

G1/S - checks for size, growth factors, nutrients, DNA damage; G2/M - checks DNA has been properly replicated; spindle assembly - checks chromosomes have correctly attached to spindle fibres

State three purpose of mitosis in life cycles

Asexual reproduction; growth; tissue repair; replacement of cells

Describe the main events of phophase

Nuclear envelope breaks down; chromatin condenses (DNA supercoils); nucleolus disappears; spindle fibres start to form from centrioles

Describe the main events of metaphase

Chromosomes line up along equator (metaphase plate); spindle fibres attach through centromeres

Describe the main events of anaphase

Sister chromatids pulled to opposite poles of the cell by shortening tubulin spindle fibres

Describe the main events of telophase

Nuclear envelope reforms around each set of chromosomes; chromatin relaxes; nucleolus reappears

Describe how cytokinesis differs between dividing animal cells and plant cells

Animal cells - cleavage furrow forms and plasma membrane is pulled inwards, splitting the cytoplasm; plant cells - vesicles assemble around metaphase plate and fuse; new plasma membrane and cellulose cell wall are laid down

Why would we use the root tip for investigating mitosis?

It is the location of meristematic tissue (source of stem cells) in a plant, i.e. cells are actively dividing

Explain why we warm the root tips in hydrochloric acid when preparing a root tip squash

To break the links between cellulose cell walls in plant cells; this ensures the stain penetrates the cells and binds to the chromosomes

Which stain would we use to stain chromosomes in a root tip squash?

Acetic orcein

What is meiosis?

The formation of gametes. Genetically unique with half the genetic information of a somatic cell.

Describe how meiosis produces genetic variation in the gametes produced

Crossing over in prophase I; independent assortment in metaphase I; independent assortment in metaphase II

Describe the difference between anaphase I and anaphase II

In anaphase I, a homologous pair of chromosomes is separated so the chromosome number halves (2 haploid cells made); in anaphase II, sister chromatids of each chromosome are separated so chromosome number stays the same (haploid number maintained)

In which stage of meiosis is the chromosome number halved

Anaphase/telophase I

Explain why genetic variation is important for a population of organisms

More likely that some individuals are adapted to a change in the environment, so the population can survive

What is differentiation?

The process by which a cell develops to become more distinct in form and function

Describe and explain how erythrocytes are adapted for their function

Very small so have a large SA:vol (biconcave shape also ensures this) meaning oxygen can reach all regions inside the cell; well-developed cytoskeleton allows the erythrocytes to change shape and move through very narrow capillaries; no nucleus or organelles so more space for Hb molecules

Explain why a neutrophil contains many lysosomes

These contain hydrolytic enzymes which digest pathogens

Describe and explain how sperm cells are adapted for their function

Acrosome in head contains enzymes to penetrate the egg follicle during fertilisation; many mitochondria to generate ATP for flagellar movement; large haploid nucleus in head to fertilise haploid ovum

Describe how guard cells open in sunny conditions

Light energy --> ATP; ATP used to actively transport potassium ions from epidermal cells into guard cells; water potential of guard cells lowered; water moves in by osmosis and guard cells become turgid

Describe the purpose of cytoskeleton threads and motor proteins in palisade cells

Moves the chloroplasts to areas of appropriate light intensity

Describe how a root hair cell plasma membrane is adapted for transport of mineral ions

Contains specialised carrier proteins to transport specific mineral ions in by active transport

Describe how cartilage is adapted for its function

Connective tissue that contains elastin and collagen fibres; prevents ends of bones from rubbing together

Define the term tissue

A group of cells working together to perform a particular function

State three types of muscle tissue, giving an example of where each is found

Skeletal - bicep/tricep etc.; smooth - digestive tract, blood vessels; cardiac muscle - heart walls

Give four features of meristematic cells that means they can differentiate easily

Thin walls with very little cellulose; no chloroplasts; no large vacuole; divide by mitosis and have the ability to differentiate into many cell types

Describe the differences between multipotent, pluripotent and totipotent stem cells

Multipotent - found in bone marrow and can form a range of different cells including blood cells; pluripotent - found in early embryos (embryonic stem cells) and can form all tissue types except extra-embryonic cells; totipotent - found in first 16 cells post-zygote and can form all tissue types including extra-embryonic tissue (e.g. placenta, umbilical cord)

State three characteristics of stem cells

Undifferentiated; all genes able to be expressed; self-renewing; able to differentiate into any cell type