Monday, 21 January 2013

2.15 understand the factors that affect the rate of movement of substances into and out of cells, to include the effects of surface area to volume ratio, temperature and concentration gradient

Surface area
with a larger surface area- molecules have more surfaces through which to diffuse, this increases the rate of moment

Increased temperature means increased kinetic energy- this will mean molecules collide with the cell membrane more often making movement through it more likely

Concentration gradient
This is the difference between the concentration inside and outside of the cell. The bigger the difference is the more opportunity molecules have of diffusing.

2.14 understand the importance in plants of turgid cells as a means of support

A turgid cell is one that is, effectively, full of water; this increases the volume of the cytoplasm, which exerts pressure outwards. These cells are stronger so they support the plant- meaning that a plant grows upwards.

This is why a dehydrated plant will wilt.

2.13 understand that movement of substances into and out of cells can be by diffusion, osmosis and active transport

These three processes (defined in 2.12) are the ways in which substances move in and out of cells.
This video explains how:

2.12 understand definitions of diffusion, osmosis and active transport

Diffusion is when molecules move from a area of high concentration to a area of low concentration

Osmosis is the movement of water, it follows the rule that water will move from a dilute solution to a concentrated solution.

Active transport is molecules being moved from an area of low concentration to an area of high concentration  energy is needed to make this happen hence 'active'

Thursday, 3 January 2013

2.11 describe experiments to investigate how enzyme activity can be affected by changes in temperature.

  • Put starch into a test tube; either heat or cool it.
  • Add amylase
  • With this mixture on white tiles, add iodine
  • Time how long it takes for the iodine to stop being blue black
  • Repeat at different temperatures and compare
When the iodine stops being blue/black there is no starch present, so it must have been digested by the enzymes.

2.10 understand how the functioning of enzymes can be affected by changes in active site caused by changes in pH

Change in PH can denature enzymes by breaking the bonds that  hold the structure in place. So the active site no longer fits with the the substrate it is meant to be breaking down. The PH at which this happens is different for different enzymes, but generally an extreme PH will denature any enzyme.

2.8 understand the role of enzymes as biological catalysts in metabolic reactions

Enzymes lower the activation energy of a reaction- making it faster- and they are unchanged from begining to end of a reaction. These two things mean its a catalyst.

For information on enzymes this is a great source:

2.9 understand how the functioning of enzymes can be affected by changes in temperature, including changes due to change in active site

As heat increases kinetic energy increases, this means enzymes and substrates more around more so they are more likely to 'bump into' one another (collide) and bind. This means that as heat increases so does the amount of reactions an enzyme catalyses.

However if the temperatures are too high it will denature enzymes, so they can't function. Because the energy breaks the bonds that hold the shape of the enzyme: without these the structure will be distorted, which will mean the active site won't be able to bind with the substrate to break it down.

Note the active site is the area on an enzyme that binds with a substrate to break it down; it is the lock in the lock and key theory.

Optimum temperature is in between these two scenarios, where there is lots of energy from heat but not enough to denature the enzyme. It is different for different enzymes.

2.7 describe the tests for glucose and starch

Test for glucose
Heat object with Benedict’s or Fehling’s Reagent.
if it turns from blue to orange then glucose is present.

The starch test
Apply iodine to the object you are testing,
if it turns from red to blue/black then there is starch.
Note: in an exam you are safest saying blue/black instead of blue or black.

2.6 describe the structure of carbohydrates, proteins and lipids

as large molecules made up from smaller basic units

Simple sugars- monosaccharides-such as glucose are the basic carbohydrates
They join together to make more complex disaccharides and polysaccharides: 

are made up of amino acids
amino acids differ depending on what the 'r' (rest) is:
Lipids, Carbohydrates, and Proteins

are made from combining glycerol and three fatty acids:
Lipids, Carbohydrates, and Proteins

The following video is quite good to watch, but it has a lot of extra content:

2.5 identify the chemical elements present in carbohydrates, proteins and lipids

Carbohydrates and lipids (fats and oils) are both made up of:

  • Carbon
  • Hydrogen
  • Oxygen

Proteines consist of:
  • Carbon
  • Hydrogen
  • Oxygen
  • Sulphur
  • Phosphorous
  • Nitrogen

2.4 compare the structures of plant and animal cells.

Plant cells have a vacuole
Plant cells have chloroplasts
Plant cells have a cell wall

They have a nucleus
They have cytoplasm
They have a cell membrane

2.2 describe cell structures, including the nucleus, cytoplasm, cell membrane, cell wall, chloroplast and vacuole

What you need to know for this is the layout of the cell, this is easiest done by diagram, but here are explanations:

Animal cell
A nucleus is in the centre of the cell; it is surrounded by cytoplasm; around the outside edge is the cell membrane.

Plant cell
A vacuole in the centre is surrounded by cytoplasm; with in this is the nucleus and chloroplasts; surrounding this is the cell membrane; and around that is the cell wall.

There are diagrams at the bottom of this page:

2.3 describe the functions of the nucleus, cytoplasm, cell membrane, cell wall, chloroplast and vacuole

Within a cell there are different organelles, the above are as such.

The nucleus, often thought as as the centre of a cell, contains all the genetic 
information of a cell (the cells chromosomes), it controls the activities of the cell.

Cytoplasm surrounds the nucleus within the cell walls. It is where reactions take place in the cell.

The cell membrane controls the movement of chemicals in and out of the cell.

The cell wall, which is made up of cellulose, strengthens the cell.

Chloroplast contain chlorophyll, and are used in photosynthesis.

Vacuole keeps the cell turgid (basically keeps the cell  filled with water.)

2.1 describe the levels of organisation within organisms: organelles, cells, tissues, organs and systems.

Organelles are highly organised structures of molecules. They have a specific function within a cell. Mitochondria is an example, generating energy for our bodies cells.

Cells are made up of Organelles, described as a functional unit, they are the basis of living things.

Tissues are a collection of similar cells all serving a common function.

Organs are made up of several kinds of tissues together forming a functioning unit.

Systems are several organs forming an organ system. Like the cardiovascular system is made up of the heart, blood and blood vessels.

This animation sums up the above nicely, worth a watch:

1.3 recall the term ‘pathogen’ and know that pathogens may be fungi, bacteria, protoctists or viruses.

Pathogens are micro-organisms that cause disease.

Bacteria, fungi, viruses and protoctists all cause disease in a variety of ways.
For example, bacteria release toxins. Another useful example of pathogens causing disease is viruses destroying host cells.

1.2 describe the common features shared by organisms within the following main groups

  • plants
  • animals
  • fungi
  • bacteria
  • protoctists
  • viruses

for each group describe examples and their features
(details of lifecycle and economic importance are not required)

Multicellular organisms
Their cells contain chloroplasts- able to carry out photosynthesis
Their cells have cellulose cell walls
They store carbohydrates as starch or sucrose
Examples include flowering plants, such as a cereal (for example maize), and a herbaceous legume (for example peas or beans)

These are multicellular organisms
They have no cell walls
They usually have nervous coordination and are able to move from one place to another
They often store carbohydrate as glycogen
Examples include mammals (for example humans) and insects (for example mosquito)

Usually organised into a mycelium made from thread-like structures called hyphae, which contain many nuclei
Some examples are single-celled
Their cells have walls made of chitin
They feed by extracellular secretion of digestive enzymes onto food material and absorption of the organic products (saprotrophic nutrition)
They may store carbohydrate as glycogen
Examples include Mucor (hyphal example) and yeast (single cell example)

These are microscopic single-celled organisms
They have a cell wall, cell membrane, cytoplasm and plasmids
They lack a nucleus but contain a circular chromosome of DNA
Some bacteria can carry out photosynthesis but most feed off other living or dead organisms
Examples include Lactobacillus bulgaricus (used in the production of yoghurt from milk) and Pneumococcus (pathogen causing pneumonia)

These are microscopic single-celled organisms
Some, like Amoeba, that live in pond water, have features like an animal cell
Some like Chlorella, have chloroplasts and are more like plants
A pathogenic example is Plasmodium, responsible for causing malaria

These are small particles, smaller than bacteria
They are parasitic and can reproduce only inside living cells
They infect every type of living organism
They have a wide variety of shapes and sizes
They have no cellular structure but have a protein coat and contain one type of nucleic acid, either DNA or RNA
Examples include the tobacco mosaic virus,  the influenza virus (causes ‘flu’) and the HIV virus (causes AIDS)

1.1 Understand that living organisms share the following characteristics:

  • they require nutrition
  • they respire
  • they excrete their waste
  • they respond to their surroundings
  • they move
  • they control their internal conditions
  • they reproduce
  • they grow and develop.

What you need to know is that to be a living organism you must do all of the above.

A good way to remember this is a pneumonic: Mrs C. Gren is one example, trying to think of the colour sea green may help.


Here, C can be replaced by H to represent homoeostasis (control of internal conditions).