Edexel GCSE Biology

1.1 What are the 7 characteristics of living organisms?

M ovement

R eproduction

S ensitivity (respond to their surroundings)

N utrition

E xcretion (of waste)

R espiration

G rowth (and development)

H omeostasis (control internal conditions)

In addition, all living organisms contain nucleic acids (DNA) and have the ability to control their internal conditions. Finally, all living organisms can die.

1.2 Variety of living organisms:

What are the unique characteristics of plants (with examples)?

- Multicellular organisms

- Cells contain chloroplasts, and are able to carry out photosynthesis

- Cells have cellulose cell walls

- Store carbohydrates as starch or sucrose

E.g. flowering plants- cereal (for example maize), herbaceous legumes (for example peas or beans)

What are the unique characteristics of animals (with examples)?

- Multicellular organisms

- Cells do not contain chloroplasts, and are not able to carry out photosynthesis

- No cell walls

- Usually have nervous coordination

- Able to move from one place to another

- Store carbohydrate as glycogen

E.g. mammals (for example humans) and insects (for example housefly and mosquito)

What are the unique characteristics of fungi (with examples)?

- Not able to carry out photosynthesis

- Usually organised into mycelium made from thread-like structures called hyphae, which contain many nuclei

- Some are single-celled

- Cells have walls made of chitin

- Feed by saprotrophic nutrition

- Store carbohydrate as glycogen

E.g. Mucor, which has the typical fungal hyphal structure, and yeast, which is single-celled

How do fungi feed?

Feed by extracellular secretion of digestive enzymes onto food material and absorption of the organic products, known as saprotrophic nutrition

What are the unique characteristics of bacteria (with examples)?

- Microscopic single-celled organisms

- Have a cell wall, cell membrane, cytoplasm and plasmids

- 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

E.g. Lactobacillus bulgaricus, a rod-shaped bacterium used in the production of yoghurt from milk, and Pneumococcus, a spherical bacterium that acts as the pathogen causing pneumonia

What are the unique characteristics of protoctists (with examples)?

- Microscopic single-celled organisms

E.g. Some, like Amoeba, that live in pond water, have features like an animal cell, while others, like Chlorella, have chloroplasts and are more like plants. A pathogenic example is Plasmodium, responsible for causing malaria

However, some protoctisis are multicellular (e.g. seaweeds)

What are the unique characteristics of viruses (with examples)?

- Small particles, smaller than bacteria

- Parasitic and can reproduce only inside living cells

- Infect every type of living organism

- Wide variety of shapes and sizes

- No cellular structure but have a protein coat and contain one type of nucleic acid, either DNA or RNA

E.g. tobacco mosaic virus that causes discolouring of the leaves of tobacco plants by preventing the formation of chloroplasts, the influenza virus that causes 'flu' and the HIV virus that causes AIDS

Describe the key unique features of viruses.

The Envelope is used to gain entry into host cells.

The Capsid is a protein coat and is used to protect the genetic information and give the virus structure.

The DNA or RNA (a different type of nucleic acid) contain the code for building new viruses.

1.3 What are pathogens?

Pathogens are organisms that may causes disease, which may be fungi, bacteria, protoctists or viruses.

2.1 What are organisms made of (what is the hierarchy)?

Organisms are made from organizations of smaller structures.

1) Organelles

2) Cells

3) Tissues

4) Organs

5) Organ systems

What are organelles?

Intracellular structures that carry out specific functions within a cell.

What are cells?

The basic structural and functional unit from which all biological organisms are made.

What are tissues?

A group of specialized cells, which are adapted to carry out a specific function.

What are organs?

A collection of two or more tissues, which carries out a specific function or functions.

What are organ systems?

A group of two or more organs.

2.2 / 2.3 Cell structures and their functions:

What is the nucleus?

The large, membrane-bounded organelle containing the genetic material of a cell, in the form of multiple linear DNA molecules organised into structures called chromosomes. The nucleus controls cellular activities such as metabolism, growth and reproduction, by regulating gene expression.

What is the cytoplasm?

In eukaryotic cells, the cytoplasm is the area between the cell membrane and the nucleus. It contains a viscous substance, holding the organelles, enclosed by the cell membrane. The functions of cell expansion, growth, metabolism and replication occur here.

What is the cell membrane?

The lipid outer covering of the cell, a protective barrier between the cytoplasm and the external environment. It is selectively permeable, controlling the exchange of the required reactants and waste products for chemical reactions within the cell. It also retains the structure of the cell.

What is the cell wall?

A wall that forms externally to the cell membrane, retaining the cells' rigidity, strength, osmotic pressure and protection against mechanical stress. It is found in plants (cellulose), fungi (chitin) and bacteria.

What is the vacuole?

A membrane-bound vesicle found in the cytoplasm of a cell, whose function includes excretion, storage and digestion.

What is the chloroplast?

A plant organelle containing chlorophyll, a light-absorbing green pigment, carrying out the process of photosynthesis.

2.4 Plant and animal structures:

Describe the structure of a plant cell.

- Square shape

- Contains the organelles:

1) Sap vacuole

2) Chloroplasts

3) Cell wall

4) Cell membrane

5) Nucleus

6) Cytoplasm

7) Mitochondria

Describe the structure of an animal cell.

- No fixed shape

- Contains the organelles:

1) Cell membrane

2) Nucleus

3) Cytoplasm

4) Mitochondria

Comparison of plant and animal cell.

Animal cell:

- No fixed shape

- Roughly 50 чm long

Plant cell:

- Rectangular shape

- Roughly 150 чm long

- Unique organelles:

1) Sap vacuole

2) Chloroplasts (chlorophyll)

3) Cell wall

N.B. The cells are measured in чm (micrometers). One micrometer is 1/1000th of a millimetre.

2.5 What chemical elements are present in carbohydrates?

- Carbon

- Hydrogen

- Oxygen

What chemical elements are present in proteins?

- Carbon

- Hydrogen

- Oxygen

- Sulphur

- Phosphorous

- Nitrogen

What chemical elements are present in lipids (fats and oils)?

- Carbon

- Hydrogen

- Oxygen

2.6 Structure of the food groups:

What is the general structure of carbohydrates, proteins and amino acids?

The structure of carbohydrates, proteins and lipids are large molecules (polymers) made up from smaller basic units (monomers).

What are carbohydrates composed of (monomers)?

Starch and glycogen (polymers of glucose)

What are proteins composed of (monomers)?

Amino acids (polymers)

What are lipids composed of (monomers)?

The three fatty acids and glycerol joined together.

2.7 What is the test for lipids?

The Emulsion test

- Ethanol solution

- Clear --> cloudy

What is the test for proteins?

The Biuret test

- Blue --> purple

What is the test for starch?

using Iodine solution

- Yellow --> blue black

What is the test for glucose?

The Benedict's test

- Benedict's solvent and heat

- Blue --> brick red precipitate

2.8 What are enzymes?

Enzymes are biological catalysts, increasing the rate of metabolic reactions.

- Are proteins

- Are specific to one particular substrate

- Are affected by temperature and pH

- Are not used up in the reaction they catalyze

2.9 How can the functioning of enzymes be affected by changes in temperature?

1. Initially, raising the temperature increases the rate of reaction due to the increased kinetic energy of the enzymes and substrates.

2. However, after the optimum temperature (37oC) is reached the enzyme begins to change shape and the active site stops being able to bind to the substrate.

3. The enzyme becomes denatured and stops working (the rate of reaction is zero at this point).

2.10 How can the functioning of enzymes be affected by changes in pH?

1. Initially, increasing the pH increases the rate of reaction.

2. However, after the optimum pH is reached the enzyme begins to change shape and the active site stops being able to bind to the substrate.

3. The enzyme becomes denatured and stops working (the rate of reaction is zero at this point).

2.11 Give an example of an experiment on the effect of temperature on enzyme function.

An example is the enzyme Catalase, which breaks Hydrogen peroxide into Water and Oxygen;

2H2O2 O2 + 2H2O

Catalase is found in potatos. Therefore, putting potato chips into peroxide will produce O2. The rate of reaction is, therefore, proportional to the volume of O2 given off. Changing the temperature will alter the volume (i.e. initially increase it, reach an optimum, then decrease quickly as the Catalase becomes denatured).

2.12 Diffusion, osmosis and active transport:

Define diffusion.

The movement of gas/liquid particles from an area of high particle concentration to an area of low particle concentration, down the concentration gradient.

Define osmosis.

The movement of water particles from an area of high water particle potential to an area of low water particle potential, across a selectively permeable membrane, down the concentration gradient.

Define active transport.

The movement of a substance against its concentration gradient (i.e. from an area of low particle concentration to an area of high concentration) using energy.

2.13 How can the movement of substances into and out of cells occur?

Through diffusion, osmosis and active transport.

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

Plant cells are normally turgid (swollen full of water). This is important because it provides strength to plants. Plant cells have a cell wall to stop them bursting when turgid. When plant cells start to lose water they become flaccid. Flaccid plants lose their strength and start to wilt. Eventually, flaccid cells become plasmalysed as the cell membrane begins to peel away from the cell wall. This kills the cell.

2.14 How can the rate of movement of substances into and out of cells be increased (affected)?

Diffusion and osmosis occur because molecules have kinetic energy. The molecules constantly bounce off each other all the time, gradually spreading out. Eventually there will be an even mixture of molecules, which is called an equilibrium. Diffusion can be affected by;

- temperature (increases Kinetic energy - 37*C)

- stirring (increases Kinetic energy)

- surface area for diffusion

- thickness / distance molecules have to diffuse

- the size of the concentration gradient

- the surface area to volume ratio (villi, microvilli)

2.16 Experiments for diffusion and osmosis:

Describe the experiment for diffusion in an artificial system.

HCl and NH3

The particles from the NH3 and HCl diffuse towards each other along the glass tube. Where they meet and react a white cloud of NH4Cl forms. The NH3 has a lighter relative mass, meaning it diffuses faster, and HCl has a heavier relative mass, meaning it diffuses slower. Ultimately, the white cloud of NH4Cl, forms closer to NH3, as the gas travels slower.

Or ink chromatography, diffusion of leaf

Describe the experiment for osmosis in an artificial system.

Iodine in visking tubing

Place starch in visking tubing within a beaker of iodine. By osmosis, the iodine will diffuse from an area of high water concentration, the hypertonic solution of the iodine in the beaker, to an area of low water concentration, the hypotonic solution of the starch in the visking tubing across the selectively permeable membrane, reacting with the starch to turn from a milky colour to dark blue.

Describe the experiment for osmosis in a biological system.

Potato cylinders

Place equal cylinders of potato tissue in varying concentrations of sucrose solution. The cylinders in the largest concentrations of sucrose should experience osmosis the most, expanding in size, while the cylinders in the smallest concentrations of sucrose will shrink. This is because the water molecules are travelling across the selectively permeable membrane of the potato to the area with least water molecules, the most hypotonic solution, relative to the hypertonic solution.

2.17 Describe the process of photosynthesis.

Photosynthesis is a chemical process whereby incoming light from the sun is absorbed and the energy used to transform carbon dioxide and water into glucose and oxygen.

Photosynthesis is highly important in the conversion of light energy to chemical energy.

2.18 What is the word equation for photosynthesis?

Carbon dioxide + Water --light--> Glucose + Oxygen

What is the chemical equation for photosynthesis?

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

What do plants use glucose for?

- Respiration

- Stored as Starch

- Turned into Cellulose (cellulose is a polymer of glucose)

- Used to make fats and oils

2.19 How does varying carbon dioxide concentration, light intensity and temperature affect the rate of photosynthesis?

At any point the rate of photosynthesis can be increased by adding more CO2, more water, more light or heating towards optimum temperature (photosynthesis is catalyzed by enzymes). However, at a certain point the addition of more e.g. light will not increase the rate of photosynthesis any further. This is because a second factor is limiting the rate of photosynthesis. Adding more of the rate- limiting factor will increase the rate further until another factor becomes limiting.

2.20 Describe the structure of the leaf.

Structures include:

- Stomata

- Guard cells

- Waxy cuticle layer

- Upper epidermis

- Mesophyll cells:

- Palisade mesophyll

- Spongy mesophyll

- Vascular bundle:

- Xylem

- Phloem

- Air spaces

- Lower epidermis

How is the leaf adapted for photosynthesis?

Cuticle - Stops the leaf from losing water (remember, water is used in photosynthesis)

Epidermis - Transparent protective layer. Protects the leaf without inhibiting photosynthesis.

Palisade cells - Are packed full of chloroplasts. Are long and thin so light has to pass through as many chloroplasts as possible.

Air Spaces - Increase the surface area inside the leaf to maximise gas exchange across the surface of the Spongy Mesophyll cells

Stoma - Allow exchange of CO2 and O2

Guard Cells - Allow the stoma to open and close to stop the leaf losing too much water

Vein (containing Xylem) - Brings a steady supply of water to the leaf.

2.21 What do plants require for growth?

Mineral ions

What are magnesium ions used for?

forms part of the chlorophyll molecule

What are nitrate ions used for?

used to make amino acids for use in plant proteins

What are potassium ions used for?

essential for cell membranes

What are phosphate ions used for?

essential part of DNA and cell membranes

2.22 Describe an experiment to investigate photosynthesis by showing the evolution of oxygen from a water plant.

Using pond weed (Elodea) which produces bubbles of O2 as it photosynthesizes. The rate of bubble production is approximately proportional to the rate of photosynthesis. Therefore, when you add light or give it more CO2, the rate of bubble production increases.

Describe an experiment to investigate photosynthesis by showing the production of starch and the requirements of light, carbon dioxide and chlorophyll.

Geranium plant. It's leaves normally turn blue-black in the presence of iodine solution showing starch is present (you have to boil it in ethanol first to remove the chlorophyll to show the colour). However, if one leaf is put in aluminum foil and another is kept with lime water both do not turn blue-black, implying both CO2 and light are essential for starch production and, therefore, essential for photosynthesis.

2.23 What should a balanced diet include?

Appropriate proportions of carbohydrate, protein, lipid, vitamins, minerals, water and dietary fibre.

2.24 What are some sources of carbohydrates?

- Potatoes

- Bread

- Pasta

- Rice

What is the function of carbohydrates?

Made from single sugars or chains of sugars. They are used in respiration to provide energy.

What are some sources of proteins?

- Meat

- Fish

- Nuts

- Quinoa

What is the function of proteins?

Broken down into amino acids, which our body absorbs and assembles into new proteins. The proteins are used for growth and repair.

What are some sources of lipids (fats and oils)?

- Butter

- Lard

What is the function of lipids?

Used as a long-term energy store (much easier to store than carbohydrates). Per mass lipids have about 10x more energy in them than carbohydrates. Also have a role in protection and insulation.

What are some sources of vitamin A?

- Carrots

- Fish

- Cheese

- Eggs

What is the function of vitamin A?

It forms an essential part of the pigment in rods and cones that detects light.

What can lack of vitamin A cause?

Lack of Vitamin A can lead to blindness.

What are some sources of vitamin C?

- Citrus fruits

- Vegetables

What is the function of vitamin C?

It forms an essential part of collagen protein, a connective protein which makes up the skin, hair, gums and bones.

What can lack of vitamin C cause?

Lack of Vitamin C causes scurvy.

What are some sources of vitamin D?

- Oily fish

- Sunlight

What is the function of vitamin D?

Aids calcium absorption in the small intestine, to regulate the growth of bones.

What can lack of vitamin D cause?

Lack of Vitamin D can cause rickets.

What are some sources of calcium?

- Dairy products

What is the function of calcium?

It is essential for bone and teeth growth and muscles.

What can lack of calcium cause?

Lack of calcium can lead to osteoporosis.

What are some sources of iron?

- Liver

- Spinach

- Red meat

What is the function of iron?

Haemoglobin formation (part of haemoglobin).

What can lack of iron cause?

Lack of iron can cause anaemia.

What are some sources of water?

- Water

What is the function of water?

Essential as a solvent for chemical reactions (e.g. cytoplasm), heat loss (e.g. transpiration), transport (e.g. blood).

What are some sources of dietary fibre?

- Wholegrain carbohydrates

What is the function of dietary fibre?

Regulates bowel movement. Sloughs off old lining of intestine.

How is the energy in food measured?

The energy in food is measured in Calories (equivalent to 4.2 kJ).

How many calories do males need to consume daily?

2500 calories

How many calories do females need to consume daily?

2000 calories

2.25 When do energy requirements vary?

Energy requirements vary with:

- Activity levels (exercise)

- Age (growing, old)

- Pregnancy

- Illness

What are the two types of digestion (briefly describe)?

- Mechanical Digestion: digestion by physically breaking food into smaller pieces (i.e. not using enzymes). Carried out by:

- mouth and teeth chewing food

- stomach churning food

- Chemical Digestion: digestion using enzymes

2.26 Alimentary canal structure and functions:

Define the alimentary canal.

The tubular, muscular, digestive tract where bolus passes through, from the mouth to the anus, allowing the nutriment to be digested and absorbed into the blood, yet the indigestible eliminated as waste. It functions by ingestion, digestion, absorption of food and water and egestion.

Define the mouth.

The oral cavity located at the beginning of the alimentary canal, through which food and air enters the body. Mechanical digestion, by the teeth, increasing surface area, and chemical digestion by the enzyme, amylase occur here.

Define the oesophagus.

A long hollow muscular tube, connecting the pharynx to the stomach, through which food passes by the process of peristalsis.

Define the stomach.

A muscular organ, situated between the oesophagus and duodenum, producing gastric juice, containing hydrochloric acid, which breaks down proteins. Mechanical digestion, by the muscle contractions of the cell wall, and chemical digestion, by the enzyme, pepsin, occur here. This prepares the bolus for further breaking down and absorption in the duodenum.

Define the pancreas.

The glandular structure involved in the secretion of pancreatic enzymes: protease, trypsin, carbohydrase and lipase, into the duodenum to act as a biological catalyst in complex protein and fats digestion. It is situated just below the stomach, in connection to the duodenum.

Define the small intestine.

The tubular digestive organ, where most food is broken down absorbed and into the organism, specifically, maltose down into glucose, due to the secretion of digestive enzymes, namely maltase. It is situated between the stomach and large intestine , with three sections: duodenum, jejunum and the ilium.