A Level OCR A Biology || Foundations in Biology (Module 2)

What is the primary function of a light microscope?

To create a colored, two-dimensional image by passing light through a specimen.

What type of image does a scanning electron microscope produce?

A black and white, three-dimensional image.

What is a key characteristic of transmission electron microscopes?

They create a black and white, two-dimensional image by passing electrons through a very thin specimen.

Why must electron microscopes operate in a vacuum?

Electrons are absorbed by air, which would interfere with imaging.

What is a dry mount in microscopy?

A method where a cover slip is placed on top of a specimen at an angle to reduce air bubbles.

Describe the process of creating a wet mount.

A drop of water is placed on the specimen before enclosing it with a cover slip at an angle.

What is the purpose of an eyepiece graticule?

To measure the length of the specimen being observed under a microscope.

How do you calibrate an eyepiece graticule?

Align the stage micrometer with the eyepiece graticule and count how many divisions fit into one micrometer division.

What is differential staining?

Using multiple stains that bind to specific cell structures to enhance visibility and identification.

What is compartmentalization in cell structure?

The separation of different parts of the cell with different functions using membranes.

What is the function of the nucleus?

Site of DNA replication and transcription, and ribosome synthesis.

What are cilia and their functions?

Hair-like projections that can be mobile, moving substances, or stationary, serving sensory functions.

What is the structure of centrioles?

Made of microtubules arranged in a 9+2 structure, occurring in pairs to form a centrosome.

What is the role of the cytoskeleton?

Provides mechanical strength, maintains cell shape, and aids transport within the cell.

What are microfilaments made of?

Actin, and they are involved in whole cell movement and contraction.

What is the function of microtubules?

They form a scaffold for cell shape and structure and act as tracks for organelle movement.

What is the rough endoplasmic reticulum (RER) responsible for?

Initial processing, folding, and packaging of proteins.

What is the function of the Golgi apparatus?

Processes and packages proteins and lipids, and produces lysosomes.

What is the main function of mitochondria?

Site of aerobic respiration, containing enzymes needed for respiration.

What is the composition of the cell wall in eukaryotes?

Composed of cellulose.

What is the role of chloroplasts?

Site of photosynthesis, containing thylakoids with chlorophyll.

What are ribosomes composed of?

Two subunits and are the site of protein production.

What do lysosomes contain?

Digestive enzymes for breaking down waste materials.

What are plasmids?

Circular pieces of DNA found in prokaryotic cells.

What is the function of flagella?

Used for locomotion and sometimes as sensory organelles.

What is the process of protein synthesis?

Proteins are produced on ribosomes, processed in the RER, modified in the Golgi apparatus, and packaged into vesicles.

What are prokaryotes?

Single-celled organisms, such as bacteria.

What are eukaryotes?

Organisms that can be unicellular or multicellular, including animals, plants, algae, and fungi.

What distinguishes eukaryotic cells from prokaryotic cells?

Eukaryotic cells have a true membrane-bound nucleus and membrane-bound organelles.

What is the difference between organic and inorganic ions?

Organic ions contain carbon, while inorganic ions do not.

What role does calcium play in biological functions?

Muscular contraction, formation and strengthening of bones, and as co-factors in enzymes.

What is the function of potassium in living organisms?

Nerve impulse transmission, photosynthesis, muscular contraction, and fluidity regulation.

What is the role of sodium in biological systems?

Nerve impulse transmission, stomata opening, fluidity regulation, and co-transport.

What does hydrogen determine in biological systems?

pH levels and respiration.

What is the significance of water as a biological molecule?

It acts as a solvent, metabolite, and temperature buffer, and has high cohesion and density properties.

What are carbohydrates made of?

Carbon, hydrogen, and oxygen.

What are monosaccharides?

The simplest sugars and fundamental building blocks of carbohydrates, such as alpha and beta glucose.

What is a disaccharide?

A molecule formed from two monosaccharides joined by glycosidic bonds.

Give an example of a disaccharide.

Maltose, sucrose, or lactose.

What are polysaccharides?

Molecules formed from many monosaccharides joined together.

What is glycogen?

The main energy storage molecule in animals, formed from alpha glucose.

What is the structure of glucose?

A simple sugar with the molecular formula C₆H₁₂O₆, existing in alpha and beta forms.

What are triglycerides?

Lipids made from one glycerol molecule and three fatty acid molecules.

What are the two types of fatty acids?

Saturated (no double bonds) and unsaturated (one or more double bonds).

What is the role of phospholipids in cell membranes?

They form a bilayer that acts as a selectively permeable barrier.

What is cholesterol's function in biological systems?

It plays an essential role in cell membrane structure and function and acts as a precursor for other biological molecules.

What is the significance of water's high latent heat of vaporization?

It provides a cooling effect with minimal water loss during evaporation.

How does the structure of cellulose contribute to its function?

Cellulose consists of long, unbranched chains of beta glucose, providing structural support in plant cell walls.

What is the importance of glucose's solubility in water?

It allows glucose to be transported in blood plasma and cytoplasm.

What are microfibrils?

Strong threads made of long cellulose chains joined by hydrogen bonds, providing structural support in plant cells.

What is the main function of water in metabolic reactions?

It acts as a metabolite in condensation and hydrolysis reactions.

What is the maximum density of water, and why is it important?

Water's maximum density is at 4 degrees Celsius, causing ice to float and insulate aquatic life.

What are the properties of lipids?

Insoluble in water, soluble in organic solvents, and primarily composed of carbon, hydrogen, and oxygen.

What elements primarily compose cholesterol?

Carbon, hydrogen, and oxygen

Describe the structure of cholesterol.

Cholesterol has a rigid ring structure made of four fused carbon rings.

Is cholesterol hydrophobic or hydrophilic?

Cholesterol is largely hydrophobic but has a small hydrophilic -OH (hydroxyl) group.

How does cholesterol interact with phospholipid molecules in cell membranes?

Cholesterol fits between phospholipid molecules, stabilizing the membrane.

What role does cholesterol play at high temperatures?

It reduces membrane fluidity by preventing phospholipids from moving too freely.

What role does cholesterol play at low temperatures?

It prevents phospholipids from packing too closely together, stopping the membrane from becoming too rigid.

List three biological molecules that cholesterol acts as a precursor for.

Steroid hormones (e.g., estrogen, testosterone), Vitamin D, and bile salts.

What is a peptide bond?

A covalent bond formed between two amino acids in a protein.

What is a dipeptide?

A molecule consisting of two amino acids linked by a peptide bond.

What is a polypeptide?

A chain of several amino acids linked together.

What is the primary structure of a protein?

The sequence of amino acids that make up its polypeptide chains.

What occurs during the secondary structure of a protein?

Hydrogen bonds form between the R groups of amino acids, causing coiling (alpha helices) or folding (beta sheets).

What types of bonds are involved in the tertiary structure of proteins?

Ionic bonds, disulfide bridges, hydrophobic interactions, and hydrogen bonds.

What defines the quaternary structure of a protein?

The assembly of different polypeptide chains to form the final protein structure.

What are dimers in protein structure?

Proteins consisting of two polypeptide chains.

What are fibrous proteins characterized by?

Long strands of polypeptide chains with little or no tertiary structure, often insoluble in water.

What is the function of keratin?

It makes up hair, nails, horns, and feathers.

What is the role of collagen?

Provides structural support and forms connective tissues like tendons, cartilage, and ligaments.

What is the function of hemoglobin?

Transports oxygen throughout the body.

What is the role of insulin?

Controls blood glucose concentration.

What is the first step in the lipid test?

Add ethanol to the sample to be tested.

What indicates a positive result in the lipid test?

The solution turns milky/cloudy.

What is the positive result for the protein test?

A purple color indicates the presence of proteins.

What is the first step in testing for reducing sugars?

Add Benedict's solution and heat the mixture.

What color change indicates a positive result for reducing sugars?

The solution changes color, indicating the presence of reducing sugars.

What is the process for testing non-reducing sugars?

Add hydrochloric acid, boil, neutralize with sodium hydrogencarbonate, then add Benedict's reagent.

What is the main characteristic of non-reducing sugars?

They do not act as reducing agents in chemical reactions.

What is the primary function of DNA?

DNA is responsible for storing genetic information.

What role does RNA play in the cell?

RNA is involved in the formation of proteins.

How many polynucleotide strands does DNA have?

DNA has 2 polynucleotide strands that form a double helix and run anti-parallel.

What are the four bases found in DNA?

Adenine, Thymine, Cytosine, and Guanine.

What are the four bases found in RNA?

Adenine, Uracil, Cytosine, and Guanine.

What type of sugar is present in DNA?

Deoxyribose.

What type of sugar is present in RNA?

Ribose.

What type of bonds are formed between nucleotides in DNA?

Phosphodiester bonds between phosphate and sugar, glycosidic bonds between sugar and base, and hydrogen bonds between bases.

What is the size comparison between DNA and RNA?

DNA is long, while RNA is short.

How many hydrogen bonds do Adenine and Thymine form?

Adenine and Thymine form 2 hydrogen bonds.

How many hydrogen bonds do Cytosine and Guanine form?

Cytosine and Guanine form 3 hydrogen bonds.

What is a triplet in the context of DNA?

A triplet is a sequence of three DNA bases.

What defines a gene?

A gene is a sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chain.

What does it mean for the genetic code to be non-overlapping?

Each triplet is only read once and triplets don't share any bases.

What does it mean for the genetic code to be degenerate?

More than one triplet can code for the same amino acid, reducing the phenotypic effect of mutations.

What are start and stop codons?

Start and stop codons signal the beginning and end of protein synthesis.

What occurs during transcription?

A molecule of mRNA is made using DNA as a template.

What is the role of RNA polymerase in transcription?

RNA polymerase uses one of the DNA strands as a template to synthesize mRNA.

What happens during translation?

Amino acids join together to form a polypeptide chain using mRNA as a template.

What is the function of tRNA?

tRNA collects amino acids from the cytoplasm and carries them to the ribosome.