Biology GCSE / OCR Gateway A / Paper 1

What is the difference between eukaryotes and prokaryotes?

-Eukaryotes are complex cells (plants and animals)

-Prokaryotes are ​smaller and simpler cells (bacteria)

What sub-cellular structures do animal cells have?

Nucleus

-contains DNA, controls the cell's activities

Cytoplasm

-where chemical reactions happen, (gel-like substance)

Mitochondria

-where energy is released from respiration, contains enzymes needed for the reactions involved

Cell Membrane

-controls what goes in and out of the cell, holds the cell together, contain receptor molecules for cell communication

What sub-cellular structures do plant cells have?

Plant cells contain all of the sub-cellular structures of animal plants but also have a few extra

Cell Wall

-gives support to the cell, made of cellulose

Chloroplasts

-Contains green substance chlorophyll where photosynthesis occurs

What sub-cellular structures are present in prokaryotic cells?

Chromosomal DNA

-1 long circular chromosome that controls the cell's activities and replication

Plasmids

-small loops of extra DNA that aren't part of the chromosome, they contain genes for things like drug resistance and can be passed between bacteria

Cell Membrane

-controls what goes in and out of the cell, holds the cell together

What is resolution?

Resolution is how well a microscope distinguishes between two points that are close together.

What is the formula for magnification?

Image size / Actual size

eyepiece lens magnification

MULTIPLIED

objective lens magnification

Why do we need to take a thin slice of a specimen before using a microscope?

To allow light to go through it, which will help us see the sub-cellular structures clearly

Why do we need to stain some specimen before using a microscope?

If the specimen is transparent or colourless, a drop of stain will help us identify what is what. Different stains are used to highlight different structures.

e.g: Methylene blue for DNA

how has electron microscopy increased our understanding of how cells work?

Gives us more detail of what we are viewing and allows us to see much smaller things

What is a chromosome?

A coiled up piece of DNA that has genes that code for traits.

How is DNA structured?

DNA is made up of 2 strands forming a DOUBLE HELIX.

The strands are made up of smaller nucleotides (monomers) making DNA a polymer

What makes a nucleotide?

Sugar

Phosphate Group

Base

Each DNA nucleotide has the same sugar and phosphate group but the base on each nucleotide is the only part of the molecule that varies (G/C/A/T)

What are complementary base pairs for DNA?

G (good)

C (cats)

A (are)

T (tigers)

What is an enzyme?

A biological catalyst

-a substance that speeds up the rate of reaction without being used up

-lowers activation energy

What factors affect enzyme activity?

-Temperature

-pH

-substrate concentration

-enzyme concentration

Explain the mechanism of enzyme action? (lock and key diagram)

Enzymes have high specificity for their substrates

What does it mean for an enzyme to be denatured?

The shape of its active site is changed so that it can no longer bind to its substrate. The optimum levels of temperature and pH levels have been exceeded

What is the rate of reaction?

How fast the reactants are changed into products

How can you investigate enzyme activity?

What is respiration?

Respiration is the process of transferring energy from the breakdown of glucose

It is an EXOTHERMIC reaction, as it transfer hear out

What are the two types of respiration?

Aerobic and Anaerobic

What are the differences between anaerobic and aerobic respiration?

Aerobic (plenty of oxygen)

-glucose+oxygen = carbon dioxide+water

-c6h12o6 + 6O2 = 6CO + 6H2O

-32ATP made

Anaerobic

-glucose=ethanol+carbon dioxide (plants)

-glucose=lactic acid (animals)

-2ATP made

Why is important to breakdown biological molecules?

They fuel respiration

Carbohydrates/Proteins/Lipids can be broken down so that energy can be transferred to ATP through respiration, the energy stored in ATP is then available for the cell

What is the structure of carbohydrates?

Carbohydrates (polymers) are made up of simple sugars (monomers)

-contain (carbon/hydrogen/oxygen)

What is the structure of proteins?

Proteins (polymers) are made up of amino acids (monomers)

-contain (carbo/hydrogen/oxygen/nitrogen)

What is the structure of lipids?

Lipids (fats + oils) are made from glycerol and three fatty acids

-contain (carbon/hydrogen/oxygen)

NOT POLYMERS because they don't form a long chain of repeating units

Where are these biological molecules broken down?

Carbohydrates

-mouth + small intestine

Proteins

-stomach + small intestine

Lipids

-small intestine

What is photosynthesis?

Green plant and algae trap light from the sun using its energy to make glucose

It is an ENDOTHERMIC reaction

Reaction happens in chloroplasts

What is the formula for photosynthesis?

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

carbon dioxide + water= glucose + oxygen

What are photosynthetic organisms?

.The producers of biomass for life on earth

-life processes depend on photosynthesis

How can we investigate the rate of photosynthesis?

Pondweed experiment

-oxygen production shows the rate of photosynthesis

-the faster the oxygen production, the faster the rate of photosynthesis

1)pondweed left to photosynthesise in a set amount of time, oxygen released is collected in the capillary tube

2)at the end the syringe is used to draw the gas bubble in the tube up alongside a ruler

The length of the gas bubble is measured and is proportional to the volume of O2 produced

What factors affect the rate of photosynthesis?

-Light intensity

-Carbon Dioxide concentration

-Temperature

How does light intensity affect the rate of photosynthesis?

How does carbon dioxide concentration affect the rate of photosynthesis?

How does temperature affect the rate of photosynthesis?

What is a limiting factor?

A factor that limits the rate of a reaction

What is diffusion?

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

What is active transport?

The movement of particles from an area of low concentration to an area of high concentration using ATP released during respiration

What is osmosis?

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

Why are new cells needed?

For growth and repair

What are the processes of mitosis?

Prophase

-before the cell divides, the DNA forms X-shaped chromosomes

Metaphase

-the chromosomes line up at the centre of the cell and the cell fibres pull them apart

Anaphase

-membranes form around each of the sets of chromosomes, these become the nuclei of the two new cells

Telophase

-the cytoplasm divides

What is the cell cycle?

the series of events that cells go through as they grow and divide.

Gap Phase 1

-cell grows and new cell structures and proteins are made

Synthesis

-cell replicates its DNA, so that when it splits during mitosis the two new cells will contain identical DNA

Gap Phase 2

-cell keeps growing and proteins needed for cell division are made

Mitosis

(SEE DOWN BELOW)

Why is cell differentiation important?

So that cells can become specialised for a particular function and carry out this function in the most efficient way

Are stem cells differentiated or undifferentiated?

Stem cells are undifferentiated. Depending on what instructions they are given, they can divide by mitosis to become new cells, which then differentiate

Where are stem cells found?

In early human embryos or the bone marrow of adults

In plants, stem cells are found in areas that are growing - roots + shoots

What is the function of stem cells?

To replace damaged cells

To help in the growth and development of organisms

What is the difference between embryonic and adult stem cells?

Embryonic stem cells

-Found in early human embryos

-Can turn into any kind of cell

-Important for growth + development of organisms

Adult stem cells

-Found in bone marrow of adults

-Cant turn into any cell type, only from the tissue they originally come from

-Used to replace damaged cells

How are plant stem cells different to animal stem cells?

They act like embryonic stem cells but unlike human stem cells they can divide to generate any type of cell for as long as the plant lives

e.g: the unspecialised cells can become specialised and form tissues like xylem and phloem

What factors affect the movement of substances?

Surface Area to Volume Ratio

(diffusion/osmosis/active transport is higher in cells with a larger surface area to volume ratio)

Temperature

(hotter = more energy = move faster)

Concentration Gradient

(substances move in and out of a cell faster if there's a big difference in concentration between the inside and outside of the cell)

Why is exchanging substances more difficult in bigger and more complex organisms?

It is more difficult to exchange substances as diffusion across the outer membrane is slower.

-some cells are deep inside the organism (distant)

-larger organisms have lower