AQA Biology Unit 1 notes

Notes for AQA Bio Unit 1 

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Biology Unit 1
Structure of an epithelial cell
The nucleus - contains the organisms hereditary material and controls the cells activities
o Nuclear envelope - Double membrane that surrounds the nucleus. Controls the entry and exit of
materials in and out of the nucleus. This is where reactions take place in nucleus.
o Nuclear pores - Allows passage of large molecules out of the nucleus.
o Nucleoplasm - Jelly material that makes up the bulk of the nucleus.
o Chromatin - Is the DNA found within the nucleoplasm. This is the form that chromosomes take up
when cell is not dividing.
o Nucleolous - Contained within the nucleoplasm. Manufactures ribosomal RNA and assembles
ribosomes.
Functions of the nucleus are to:
o Manufacture ribosomal RNA and ribosomes
o Retain genetic material of the cell in form of DNA or chromosomes
o Act as the control centre of the cell through production of mRNA and hence protein synthesis
Mitochondria
o Double membrane surrounds organelle. Outer membrane controls entry and exit of material, inner
membrane is folded to make cristae.
o Cristae - Shelf-like extensions of the inner membrane. Provide large surface area for attachment of
enzymes involved in respiration.
o Matrix - Makes up remainder of the mitochondrian. Contains proteins, lipids and DNA that allows
mitochondria to control production of their own proteins. Enzymes involved in respiration are found
in the matrix.
Mitochondria are responsible for production of ATP (energy carrier molecule) from carbohydrates.
Endoplasmic reticulum
o Rough Endoplasmic Reticulum (RER) - Ribosomes present on outer surface. Functions are to:
Provide a large surface area for synthesis of proteins.
Provide a pathway for the transport of material throughout the cell
o Smooth Endoplasmic Reticulum (SER) Functions are to:
Synthesise, store and transport lipids
Synthesise, store and transport carbohydrates
Golgi apparatus - the `sorting office'. Takes proteins and lipids made in the ER, completes and modifies them
and them and then packages them into small vesicles ready for export.
Functions of golgi apparatus:
o Adds carbohydrate to proteins to from glycoproteins
o Produces secretory enzymes
o Secretes carbohydrates
o Transports, modifies and stores lipids
o Forms lysosomes

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Biology Unit 1
Lysosomes - contain many digestive enzymes. Breaks down unwanted substances.…read more

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Biology Unit 1
Microscopy
Light microscope
Advantages Disadvantages
Can be used to observe living material Light has long wavelength
Material seen in natural colour Low resolution
Can't resolve object smaller than 250nm
2 Different types of electron microscope
o Transmission electron microscope (TEM) - consists of an electron gun that produces a beam of
electrons that is focused onto the specimen by a condenser electromagnet.…read more

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Biology Unit 1
µm Micrometre 10-6
nm Nanometre 10-9
Cell Fractionation - Process when cells are broken up and the different organelles are separated out. Before
cell fractionation can begin tissue must be placed in a cold, isotonic buffered solution.
o Cold - to reduce enzyme activity that might break down the organelles
o Isotonic - to prevent organelles from bursting or shrinking as result of osmotic gain or loss of water.…read more

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Biology Unit 1
Cell surface membrane is the plasma membrane that surrounds cells and forms the boundary between cell
cytoplasm and the environment. Controls movement of substances in and out of the cell.
Molecules that from this structure:
o Phospholipids from a bilayer sheet. Consists of a molecule that is composed of a fatty acid chain
at one end, and a glycerol-phosphate-nitrogen group at the other end. The phospholipids arrange
themselves in two layers, with the fatty acid chains facing each other.…read more

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Biology Unit 1
o Allow active transport across the membrane by forming ion channels for sodium and potassium
There are several methods by which molecules and ions can move across the cell membrane:
o Diffusion
o Osmosis
o Active transport
Diffusion - net movement of molecules or ions from a region where they are more highly concentrated to
one where their concentration is lower, they move down a concentration gradient. Diffusion is passive as it
does not need energy.…read more

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Biology Unit 1
Osmosis - the passage of water from a region of high water potential to a region where it has a lower water
potential through a partially permeable membrane.
Pure water has a water potential of 1 which is the highest water potential, everything is negative.
Active transport - the movement of molecules or ions into or out of a cell from a region of lower potential to
a region of higher water potential using energy and carrier molecules.…read more

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Biology Unit 1
Absorption in the small intestine
Villi and microvilli
Villi have thin walls, lined with epithelial cells on the other side of which is a rich network of blood capillaries,
they considerably increase the surface area of the small intestine and therefore accelerate the rate of
diffusion. Villi are situated at the interface of the lumen of the intestines and the blood and other tissues
inside the body. They are part of a specialised exchange surface adapted for absorption.…read more

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Biology Unit 1
Mechanism by which glucose is absorbed from the small intestine is an example of co-transport because 2
molecules are involved. -> Sodium potassium pump
Digestion is the process in which large molecules are hydrolysed by enzymes to produce small molecules
that can be absorbed and assimilated.
1. Ingestion - food is taken in the mouth
2. Digestion - enzymes break down large insoluble molecules into smaller soluble molecules
3.…read more

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Biology Unit 1
Biochemical tests
Reducing sugar
1. Add Benedicts test
2. Boil
3. Colour changes from blue to brick red. Blue if no reducing sugar is present and brick red is reducing
sugar is present
Non-reducing sugar
1. Check no reducing sugar is present (by using reducing sugar test)
2. Boil test solution with dilute hydrochloric acid
3. Neutralise with sodium hydrogen-carbonate
4. Repeat Benedicts test, you know get positive result
Starch
1. Add iodine
2.…read more

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