GCSE OCR Gateway Biology

What are eukaryotic cells?

Cells with a nucleus

What size are eukaryotic cells?

10-100 micrometers

What are prokaryotic cells?

Cells with no nucleus

What size are prokaryotic cells?

1-10 micrometers

Where is the genetic material found in prokaryotic cells?

Cytoplasm and in plasmids

State the function of the nucleus

Controls all activities of the cell, contains genetic information

State the function of mitochondria

Contains the enzymes for cellular respiration

State the function of cell membrane

Contains receptor molecules, selective barrier to control what enters cell

State the function of cytoplasm

Site of chemical reactions

State the function of ribosomes

Site of protein synthesis

Name three subcellular structures a plant cell has that an animal cell does not

Chloroplast, cell walll, vacuole

State the function of chloroplasts

Contain chlorophyll which absorbs light energy for photosynthesis to occur

Where are chloroplasts found?

Only in green parts of the plant

What is the function of the cell wall?

To protect and support the cell

What is a plants cell wall made from?

Cellulose

State the function of the vacuole

Contains cell sap which keeps the cell rigid and the plant upright

What is the cell wall in a prokaryote made from?

Peptidogylcan

State the function of flagella

Tail like structures that allow the cell to move through liquids

State the function of pili

Hairlike structures that allow the cell to attach to structures and transfer genetic material between bacteria

State the function of a slime capsule

Prevents dehydration of cell and protects it from poisonous substances. Also allows cell to stick to smooth surfaces

State the function of plasmids

Circular rings of DNA used to store extra genes

State the advantages of a light microscope

Cheap, portable, simple to prepare sample, natural colour of specimen seen, specimen can be alive

State the advantage of an electron microscope

Specimen can be viewed in higher resolution so subcellular structures can be seen

State the disadvantages of an electron microscope

Expensive, not portable, complex sample preparation, imagine in black and white, specimen must be dead

Define resolution

The smallest distance between two points that can be seen as separate entities

Describe how to observe cells through a light microscope [6]

Move the stage to its lowest position, select the objective lens with the lowest magnification, place slide with cells on it on the stage, raise stage to highest position, lower stage slowly using coarse focus knob until you see your image, turn fine focus knob slowly until object comes into clear focus.

Why do scientists stain cells?

To make the cells clearer or more visible

What does DNA stand for?

Deoxyribonucleic Acid

Define chromosome

A strand of DNA which contains genes

How many chromosomes are in each human cell

46

Define genes

Section of DNA which codes for a specific protein

What is the DNA monomer called?

Nucleotide

What does a nucleotide consist of?

Sugar, phosphate, base

What are the complementary base pairs in DNA?

A-T, C-G

Rank the following in order from smallest to largest: nucleus, cell, gene, chromosome

Gene, chromosome, nucleus, cell

Describe the structure of DNA

Two strands are joined together by complementary base pairs. Forms a double helix shape

What is the purpose of transcription?

To produce mRNA strand

Describe the process of transcription

DNA unzips, complementary base pairs pair up which forms an mRNA strand, mRNA strand leaves the nucleus, DNA zips back up

What is the purpose of translation?

To produce a protein from an mRNA strand

Describe the process of translation

mRNA strand attaches to ribosome, it is read in threes by tRNA, each triplet codes for a separate amino acid (triplet code), amino acids join together to form polymers, the chain of amino acids determines which protein will fold

What is the monomer of proteins?

Amino acids

Define enzyme

A protein which acts as a biological catalyst

State an example of when enzymes are used

Breaking down large molecules into smaller ones in digestion

What is it called when the substrate binds to the enzyme?

Enzyme-substrate complex

What is the active site?

The active site is the region on the enzyme where the substrate binds

What is the substrate?

The molecule that binds to the active site

Which factors affect enzymes?

pH, temperature, enzyme and substrate concentrations

What happens to enzymes if the conditions are too extreme?

They denature and the shape of the active site is changed so the substrate cannot bind to it

Define cellular respiration

The process in which cells make ATP by breaking down organic compounds, occurring in all mitochondria

What kind of reaction is cellular respiration?

Exothermic

Define metabolic rate

The rate at which reactions take place in the body

What are carbohydrates broken down into?

Monosaccharides

Name the monosaccharides

Glucose, fructose, galactose

Why are carbohydrates needed in the body?

Energy store

Why are proteins needed in the body?

Growth and repair of muscle tissue

What do proteins break down into?

Amino acids

What are lipids broken down into?

Glycerol and three fatty acid molecules

What enzyme breaks lipids down?

Lipase

What can happen once food molecules are completely broken down?

They are absorbed into your bloodstream and travel to the cells that need them

Define aerobic respiration

Exothermic reaction that breaks down glucose to release energy using oxygen

What is the balanced symbol equation for aerobic respiration?

C6H12O6 + 6O2 -> 6CO2 + 6H2O

What is transferred in aerobic respiration?

ATP

When does your body use anaerobic respiration?

During strenuous exercise

What is the word equation for anaerobic respiration?

Glucose -> lactic acid

Why do we normally respire aerobically?

Produces more ATP molecules per glucose molecule than anaerobic, lactic acid in anaerobic can cause cramp

Define oxygen debt

The amount of oxygen required to break down lactic acid

What is the word equation for fermentation?

Glucose --> ethanol + carbon dioxide

What organism performs fermentation?

Yeast

What can the products of fermentation be used for?

Make bread, beer, and wine

Define photosynthesis

The process by which green use sunlight to sythnesise foods from carbon dioxide and water.

What is the main producer of food on earth?

Photosynthetic organisms

How does carbon dioxide enter the plant for photosynthesis?

Diffuses from the air through the stomata and into the plant

How does water enter the plant for photosynthesis?

Enters the root from the soil by osmosis

What is the balanced symbol equation for photosynthesis?

6CO2 + 6H2O --> C6H12O6 + 6O2

Describe the two stages of photosynthesis

Stage 1 is the light dependent stage where energy transferred from light splits water molecules into oxygen gas and hydrogen ions.
Stage 2 is the light independent stage where carbon dioxide combines with the hydrogen ions to make glucose

What type of reaction is photosynthesis?

Endothermic

What do plants do with glucose if they don't need to use it immediately?

Convert it to starch

How do you test a leaf for starch?

Boil the leaf to kill it, place leaf in boiling ethanol to remove all the chlorophyll, wash the leaf, place leaf on a white tile, add a few drops of iodine. If starch is present, iodine will turn from brown to blue-black.

How do you prepare a food sample?

Get a piece of food and break it up. Transfer to a beaker and add some distilled water. Stir with glass rod. Filter solution to remove any bits of solid food.

How do you test for sugars?

Add Benedict's reagent to food sample and heat it using water bath. Turns from blue to brick red if sugars are present.

How do you test for lipids?

Add a few ml of ethanol to the food sample. If lipids are present, solution turns from clear to cloudy white.

How do you test for proteins?

Add biuret solution to food sample and shake. If proteins present, then from blue to purple.

What precaution should be taken when testing for proteins and why?

Handle the Biuret solution with care as it contains copper sulfate and sodium hydroxide

How can you test if a plant is photosynthesising?

Test it for starch

How can you prove light is needed for photosynthesis?

Take a destarched plant and cover part of its leaves with black card so light can't reach this part of the plant. Place plant in sunlight for several hours, remove the card, test the leaf for starch

How can you prove carbon dioxide is needed for photosynthesis?

Take a destarched plant, place in polythene bag, add pot of soda lime inside bag, seal bag, place plant in sunlight for several hours, test it for starch. It should be negative.

How can you prove oxygen is given off in photosynthesis?

Place upturned test tube above pondweed. Allow plant to photosynthesis until test tube is full. Test the tube for oxygen using glowing splint

How can you investigate the effects of light intensity on photosynthesis?

Take a boiling tube filled with sodium hydrogen carbonate solution and pondweed and place it 10cm away from LED light source. Count the number of bubbles given off in one minute. Repeat experiment using different distances from the light source

What is the problem with counting gas bubbles when testing light intensity in photosynthesis?

Bubbles can move too fast to count accurately and bubbles aren't always the same volume

State the inverse square law

Light intensity is directly proportional to 1/distance^2

If you double the distance from the light source in photosynthesis, what happens to the light intensity?

Falls by four times

What are the limiting factors of photosynthesis?

light intensity, carbon dioxide, and temperature

What are the benefits of using a water bath?

Reduces fire risk and temperature can be set to an exact amount

Define diffusion

The movement of particles from an area of high concentration to an area of low concentration

Give an example of diffusion

Carbon dioxide diffusing out of respiring cells

At what point is the concentration gradient zero?

When concentration of particles is the same everywhere

Why is diffusion a passive process?

Energy is not transferred

What factors would increase the rate of diffusion?

Decreasing the distance particles need to move, increasing the concentration gradient, increasing the surface area, increase temperature

Define osmosis

The movement of water molecules from an area of high water potential to an area of low water potential across a partially permeable membrane

What is water potential?

The concentration of free water molecules