Module One: Molecules, Cells and Systems

Module one for AQA specification A

HideShow resource information

Eukaryotic Cells

Eukaryotic cells are more complex and include all animal and plant cells.

Larger Cells

DNA is linear

Nucleus present - DNA inside nucleus

No cell wall (in animals), cellulose cell wall (in plants) or chitin cell wall (in fungi)

Many organelles, mitochondria present.

Larger Ribosomes

Example: Human Liver Cells

1 of 37

Prokaroytic Cells

Prokaroytic cells are more simple than eukaryotic cells. Prokaryotes include bacteria and blue-green algae.

Extremely small cells

DNA is circular

No Nucleus - DNA free in cytoplasm

Cell wall made of a polysaccharide, but not cellulose or chitin.

Few organelles, no mitochondria

Small ribosomes

Example: E. coli bacterium

2 of 37

The difference between the cells

(http://www.phschool.com/science/biology_place/biocoach/images/cells/allcell.jpg)

3 of 37

Light Microscope Show Cell Structure

This shows you the general structure of a cell.

You cannot see most of the organelles in the cell, you can see the larger organelles like the nucleus.

You can just about see the membrane along the top surface of some animals cells. it is sometimes folded to make the microvilli.

This, therefore increases the surface area for absorption substances.

E.g. Epithelial cells which line the small intestines. The microvilli help them to efficiently absorb products of digestion.

Note: Microvilli are much clearer under the electron microscope.

4 of 37

Electron Microscope Shows Cell Ultrastructure

There is not much in a cell that an electron microscope cannot see.

You can see a cell's ultrastructure which is its organelles and the internal structure of most of them.

Most of what we know about cell structures have been discovered by the use of an electron microscope.

Advantages :) Gives higer resolution than a light microscope.

Disadvantages :( has to be dead/ no colours/ very fragile/ very expensive

5 of 37

Magnification is Size, Resolution is Detail

1) Magnification is how much bigger the image is than the specimen.

2) Resolution is how detailed the image is. It is how wella microscope distinguishes between two points that are close together.

- Light microscopes have a lower resolution than electron microscopes. Decreasing the wave length of the light increases resoultion, but even then a loght microscope can only distinguish points 0.2 micrometres apart.

- Electron Microscopes use electrons instead of light to form an image and focus them with an electromagnet. You cannot see electrons, so the image has to be formed on a fluorescent screen. Electrons have shorter wave lengths than light, which means they can resolve things down to 0.5 nanometres. Therefore they provide better resolution and more detailed images.

6 of 37

The 2 types of Electron Microscope

1. Transmission electron microscope (TEM) - this uses electromagnets to focus a beam of electrons, which is then transmitted through the specimen. Denser parts of the specimen absorb more electrons, which makes them look darker on the image you end up with. TEMs are good because they provide higher resolution images, but can only be used on thin specimens.

2. Scanning electron microscope (SEM) - this scans a beam of electrons across the specimen, and reflected electrons are gathered in a cathode ray tube, which forms a TV image. The images you end up with show the surface of the specimen and they can be 3-D. SEMs provide lower resolution images than TEMs.

7 of 37

A cross section of a plant cell

(http://www.enchantedlearning.com/subjects/plants/cell/anatomy.GIF)

8 of 37

A Cross section of an animal cell

(http://www.enchantedlearning.com/subjects/animals/cell/anatomy.GIF)

9 of 37

Organelles (part I)

Cell Surface Membrane

Structure: 2 layers of phospholipid

Function: Partially permeable membrane.

Nucleus

Structure: Largest Organelle. Membrane bound and contains DNA

Function: DNA forms chromosomes. Nucleic acid leaves the nucleus when the cell makes things.

10 of 37

Organelles: (part II)

Endoplasmic Reticulum (ER)

Structure: Series of membrane bound sacs. Forms sheets called cisterine.

Function: Rough ER (with ribosomes) collects proteins manufactured by ribosomes. Smoothe ER is involved in the manufacture of lipids and steroids

Ribosomes

Structure: Very small. They are made of RNA

Function: They manufacture protein and are attached to rough ER.

11 of 37

Organelles: (Part III)

Mitochondria

Structure: Made of 2 membranes. Inner is folded to form cristae.

Function: The formation of ATP (energy), in areobic repiration.

Golgi Apparatus

Structure: Flat membranes continous with the ER and forms vesicles.

Function: Golgi processes molecules and transoprts them.

12 of 37

Organelles: (part IV)

Lysosomes

Structure: Spherical sacs of enzymes.

Function: Lysosomes break down unwanted cellular components.

Centroles

Structure:Hollow cylinders that form microtubes.

Function: Centrioles are important in cell division

13 of 37

Centrifuge

1. Homogenised - mixes it.

2. Ice cold isotonic buffer.

3. Into a test tube and spin it at a low speed.

4. Decant the supernatant.

5. Respin the supernatant at high speed.

14 of 37

Faciliated Diffusion

* Used for big molecules like glucose and amino acids

* ions Na+

Channel Proteins Carrier Proteins

(http://kentsimmons.uwinnipeg.ca/cm1504/Image133.gif) (http://kentsimmons.uwinnipeg.ca/cm1504/Image132.gif)

High to low concentration!In carrier proteins the receptor is shaped for glucose. the glucose binding causes the protein to change shape.

DO NOT USE ENERGY!!!!!!!!

15 of 37

Transport across membranes

Fick's law:

"Diffusion Rate =large surface area x difference in concentration / thickness of exchange pathway."

16 of 37

Elements found in humans

Main Elements

  • Nitrogen
  • Oxygen
  • Hydrogen
  • Carbon

Trace

  • Calcium
  • Potassium
  • Zinc
  • Magnesium
  • Iron
17 of 37

Main Food Groups

Carbohydrates - energy - C, H, O

Proteins - Growth and repair - C,H,N,O

Fats/Lipids - store of energy and insulation - C,H,O (P)

18 of 37

Misc word meanings.

Metabolism - The full set of chemical processes carried out by a living organism (i.e. anabolism and catabolism)

Anabolism - The formation of large complex molecules by linking smaller simpler molecules, (condensation reactions - form water)

Catabolism - The breakdown of large complex molecules into smaller molecules. (Hydrolysis reactions - add water)

*Anabolic reactions require energy input (Endothermic - need ATP)

* Catabolic reactions release energy (exothermic)

19 of 37

Monosaccharide

A monosaccharide or hexose is a single sugar unit

Examples of these are:

*Pentose: C5 H10 O5 --> Deoxyribose (DNA) and Ribose (RNA and ATP)

*Hexoses: C6 H12 O6 --> Glucose, Fructose and Galactose

20 of 37

Disaccharides

Disaccharides are double sugars i.e. two sugar units linked together.

  • Maltose: glucose + glucose - intermediate between glucose and starch.
  • Sucrose: glucose + fructose - transported in the pholem of plants
  • Lactose: glucose + glucose - the sugar present in milk.
21 of 37

Polysaccharides

Are loads of sugars joined together.

Multisugars - the three examples of 'polyglucoses'

* Starch: plant glucose reserve -- made of 1/2 amylose and 2/3 amlyopectin.

* Glycogen: glucose reserve of animals (liver and muscle) and fungi. Similar to amlyopectin.

*Cellulose: plant cell walls (= fibre in our diet)

22 of 37

Biochemical Tests

Starch - Iodine Test - Blue/black colour indicates starch.

Reducing Sugars - Benedicts test - Brown/red colour indicates sugar is present.

Lipids - Emulsion Test - Forming a cloudy white emulsion indicates lipids are present.

Protein - Biuret Test - Lilac/Purple indicates protein is present.

23 of 37

Transport Across Membranes

1. Diffusion

2. Osmosis is a particular kind of diffusion involving water molecules. It diffuses through a partially permeable membrane from an area of higher water potential. The molecules will diffuse both ways through the membrane. Water moves in and out of plant cells by osmosis. Sugars and ions inside the plant cell lower the water potential inside the cell, so water moves into the cell by osmosis.

3. Facilitated diffusion : see above

4. Active Transport moves substances against a concentration gradient - it uses energy to move molecules and ions across cell membranes against a concentration gradient.The molecules attach specific carrier proteins in the cell membrane.

5. Materials can be taken into cells by endocytosis this is when the cell takes in substances by surrounding them with a section of the celll membrane to form a small vacuole called a vesicle.

6. Materials can be removed from cells by exocytosis. they are secreted from cells.

24 of 37

Proteins

  • Proteins are made from long chains of amino acids
  • Proteins are formed by condensation reactions
  • Proteins have up to four structures

* The primary structure: sequence of the amino acids in the long chain that makes up the protein.

*The secondarystructure: bonds between the amino acids make the chain form a coil. The most common "spiral" is called the alpha helix

* The tertiary structure: the above structure is coiled and folded in a characteristic way that identifies the protein.

* The quarternary structure: some proteins are made of several different polypeptide chainsheld together by various bonds.

  • Proteins are either globular or fibrous. Fibrous ~ are made up of long, insoulble polypeptide chains (tertiary structure). Globular ~ are made up of polypeptide chains which are folded lots of times (tertiary structure)
25 of 37

Lipids

  • Lipids contain a lot of energy, so they make useful medium or long term energy stores. Cannot be broken down quickly.
  • Lipids stored underneath the skin in mammals act as insulation.
  • Can act as a waterproofing layer.
  • Provides physical protection.
  • Most fats are triglycerides (composed of one molecule of glycerol and three fatty acids attachted to it.
  • Triglycerides are formed by condensation reactions and are broken up by hyrolysis reactions.
  • Can be saturated ot unsaturated.
  • Phospholipids are a speical type of lipid - found in cell membranes. A phosphate group replaces one of the fatty acid molecules, ionised so therfore attract water, therfore part of the phosopholipid molecule is hydrphilic ( attracts wtaer) while the rest is hyrdophobic.
26 of 37

Action of enzymes

  • Are biological catalysts. they speed up chemical reactions.
  • catalyse every metabolic reaction in the body.
  • Are globular proteins
  • Has an area called the active site
  • Reduce Activation energy.
  • when substrate fits into the enzyme's active site it forms an enzyme substrate complex.
  • The lock and key model - specific substrates.
  • Induced fit midel - active sifte is not rigid the enzyme substrate complex changes shape slightly.
27 of 37

Factors that affect enzyme activity

  • Temperature has a big influence on enzyme activity.
  • pH also affects enzyme activity.
  • Enzyme concentration affects the rate if reaction
  • Substrate concentration affects the rate if reaction up to a point.
  • Enzyme activity can be inhibited. Molecules that bind to the enzyme that they inhibit. inhibitation can be competitive (active site directed) or non competitive (non active site directed)
  • Non competitive inhibitors bond to the enzyme away fro the active site but this causes the active site to change shape.
  • Competitive inhibitors have a similar shape to the substrate.
28 of 37

Tissues

Similar Cells are organised into tissues.

  • Epithelial tissue is a single layer of flat cells lining a surface. usually found on exchange surfaces.
  • Alveolar epithelium is an example of epithelial tissue: - the cells are thin, not much cytoplasm, short diffusion pathway. only a single layer of cells, which are flat and there are lots of them so there's a large surface area of exchange.

Blood is a tissue made up of different cells.

  • it is a liquid tissue composed of different types of cells suspended in the plasma.

Red Blood cells:

  • have no organelle/ more room for haemoglobin/ have a lrage surface area/ bi-concave disc/ elastic membrane to allow them to change shape.

White blood cells: lymphocyte(large nucleus)/monocyte(lobed nucleus)/granulocyte(granular cytoplasm and lobed nucleus)

29 of 37

Surface area to volume ratio

Smaller animals have higher surface area : volume ratio

Organisms need to exhangematerials with the enviroment.

  • Excrete waste products like co2
  • SA important for body temp
30 of 37

Organs and blood transport

Arteries: carry blood from the heart to the rest of the body. Thick walled, muscular, and have elastic tissue. can cope with high pressure. Inner lining is folded so it can expand.

Arterioles: Forma network of vessles throughout the body. Directed into different areas of demand.

Veins: Blood under lower pressure back to the heart, wider.

* Mammals have a closed double circulation

Substances are exchanged between blood and body tissues at capilllaries.

  • They are always found very near cells in exchange tissues.
  • Their walls are only one cell thick
  • A large number of capillaries to increase surface area for exchange.
31 of 37

Lipids

  • Lipids contain a lot of energy, so they make useful medium or long term energy stores. Cannot be broken down quickly.
  • Lipids stored underneath the skin in mammals act as insulation.
  • Can act as a waterproofing layer.
  • Provides physical protection.
  • Most fats are triglycerides (composed of one molecule of glycerol and three fatty acids attachted to it.
  • Triglycerides are formed by condensation reactions and are broken up by hyrolysis reactions.
  • Can be saturated ot unsaturated.
  • Phospholipids are a speical type of lipid - found in cell membranes. A phosphate group replaces one of the fatty acid molecules, ionised so therfore attract water, therfore part of the phosopholipid molecule is hydrphilic ( attracts wtaer) while the rest is hyrdophobic.
32 of 37

Action of enzymes

  • Are biological catalysts. they speed up chemical reactions.
  • catalyse every metabolic reaction in the body.
  • Are globular proteins
  • Has an area called the active site
  • Reduce Activation energy.
  • when substrate fits into the enzyme's active site it forms an enzyme substrate complex.
  • The lock and key model - specific substrates.
  • Induced fit midel - active sifte is not rigid the enzyme substrate complex changes shape slightly.
33 of 37

Factors that affect enzyme activity

  • Temperature has a big influence on enzyme activity.
  • pH also affects enzyme activity.
  • Enzyme concentration affects the rate if reaction
  • Substrate concentration affects the rate if reaction up to a point.
  • Enzyme activity can be inhibited. Molecules that bind to the enzyme that they inhibit. inhibitation can be competitive (active site directed) or non competitive (non active site directed)
  • Non competitive inhibitors bond to the enzyme away fro the active site but this causes the active site to change shape.
  • Competitive inhibitors have a similar shape to the substrate.
34 of 37

Tissues

Similar Cells are organised into tissues.

  • Epithelial tissue is a single layer of flat cells lining a surface. usually found on exchange surfaces.
  • Alveolar epithelium is an example of epithelial tissue: - the cells are thin, not much cytoplasm, short diffusion pathway. only a single layer of cells, which are flat and there are lots of them so there's a large surface area of exchange.

Blood is a tissue made up of different cells.

  • it is a liquid tissue composed of different types of cells suspended in the plasma.

Red Blood cells:

  • have no organelle/ more room for haemoglobin/ have a lrage surface area/ bi-concave disc/ elastic membrane to allow them to change shape.

White blood cells: lymphocyte(large nucleus)/monocyte(lobed nucleus)/granulocyte(granular cytoplasm and lobed nucleus)

35 of 37

Surface area to volume ratio

Smaller animals have higher surface area : volume ratio

Organisms need to exhangematerials with the enviroment.

  • Excrete waste products like co2
  • SA important for body temp
36 of 37

Organs and blood transport

Arteries: carry blood from the heart to the rest of the body. Thick walled, muscular, and have elastic tissue. can cope with high pressure. Inner lining is folded so it can expand.

Arterioles: Forma network of vessles throughout the body. Directed into different areas of demand.

Veins: Blood under lower pressure back to the heart, wider.

* Mammals have a closed double circulation

Substances are exchanged between blood and body tissues at capilllaries.

  • They are always found very near cells in exchange tissues.
  • Their walls are only one cell thick
  • A large number of capillaries to increase surface area for exchange.
37 of 37

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Cellular processes and structure resources »