BIology IGCSE Edexcel Specification in questions (copy)

Triple and Double specifications are specified. When triple it says TRIPLE before it. Please make a copy

The nature and variety of living organisms

a. Characteristics of living organisms

b. Variety of living organisms

what characteristics do all living organisms share

MRSCGREN

Movement

Respiration

sensitivity

control their internal conditions

grow and develop

Reproduction

Excrete waste

require nutrition

\

Common features shown by plants

Eukaryotic Organisms

multicellular organism

cells contain chloroplasts so can photosynthesis

cellulose cell walls

store carbohydrates as starch/sucrose

examples: Maize, peas

Common features shown by animals

Eukaryotic Organisms

Multicellular organism

have nervous co-ordination

can move from one place to another

**carbohydrates are stored as glycogen**

Examples: humans, housefly

Common features shown by fungi

Eukaryotic Organisms

most are multicellular Some are Single-celled Organism

and some have their body organised into a mycelium made from thread-like structures called hyphae (which contain many nuclei)

cell walls are made from chitin

**feed by extracellular secretion of digestive enzymes (saprotrophic nutrition)**

store carbohydrates as glycogen

examples: Mucor (hyphal structure), yeast (single celled)

Common features of a Protoctists

* Eukaryotic Organism
* Microscopic single-celled organisms
* **some aggregate** (group together) into **larger forms**, such as colonies or chains of cells that form filaments
* Their cells contain a **nucleus** with a **distinct membrane**
* some have an animal-like structure whereas
* some have chloroplasts + a cell wall and is much more like a plant cell
* plant eg. chlorella
* animal eg plasmodium

Common features shown by bacteria

Prokaryotic Organisms

microscopic single-celled organisms

they have a cell wall, cell membrane, cytoplasm, circular chromosome of dna

don’t have a nucleus

Examples: Lactobacillus bulgaricus , Pneumococcus

what is a pathogen

an organism causing disease to its host

What do pathogens include

fungi, bacteria, protoctists, viruses

what is a Virus

not living organisms

small particles, smaller than bacteria

parasitic can reproduce inside living cells, can infect every type of living organism.

Variety of shapes and sizes

no cellular structure

Examples: Tobacco mosaic virus , HIV

Structure and Function in living organisms

a. Level of organisation

b.Cell structure

c.Biological molecules

d.Movement of substance into and out of cells

e.Nutrition

f.Respiration

g.Gas exchange

h.Transport

I.Excretion

j.Co-ordination and response

Levels of Organisation in organisms

Organelles

Cells

Tissues

Organs

Organ Systems

What is an organelle

A small structure in a cell that is surrounded by a membrane and has a specific function

\

What is a cell

Basic functional and structural units in a living organism

What is a tissue

Groups of cells of similar structures working together to perform the same function

What is an organ

Made from different tissues working together to perform specific function

What is an organ system

Groups of organs with related functions, working together to perform body functions

Describe cell structures including the ; nucleus

a large organelle surrounded by a nuclear envelope (double membrane) which contains many pores. The nucleus contains chromosomes (which are made from protein-bound linear DNA.

the nucleolus is in the nucleus

Describe cell structures including the ; Cytoplasm

gel-like structure containing all the cell organisms

Describe cell structures including the ; Cell membrane

the membrane found on the surface of animal cells and just inside the cell wall of other cells. It is mainly made of lipids and protein.

Describe cell structures including the ; Cell wall

A rigid structure that surrounds cells in plants, algae and fungi. Plants and algae, its made mainly of the carbohydrate cellulose. In fungi, it’s made of chitin.

Describe cell structures including the ; Mitochondria

They are usually oval-shaped. They have a double membrane - the inner one is folded to form structures calls cristae. Inside is the matrix, which contains enzymes involved in respiration.

Describe cell structures including the ; Chloroplasts

A small, flattened structure found in plant and algal cells. It is surrounded by a double membrane, and also has membranes inside called thylakoid membranes.

These membranes are stacked up in some parts of the Chloroplasts to form grana.

Grana are linked together by lamellae - thin, flat pieces of the thylakoid membrane.

Describe cell structures including the ; Ribosomes

A very small organelle that either floats free in the cytoplasm or is attached to the rough endoplasmic reticulum. It’s made up of proteins and RNA. Its not surrounded by a membrane

Describe cell structures including the ; Vacuole

**A membrane-bound organell**e found in the cytoplasm or plant cells.

It contains **cell sap.**

The surrounding membrane is called the tonoplast.

Describe the functions of the ; Nucleus

The nucleus controls the cell's activities (by controlling the transcription of DNA). DNA contains instructions to make proteins. The pores allow substances (e.g. RNA) to move between the nucleus and the cytoplasm. The nucleolus makes ribosomes.

Describe the functions of the ; Cytoplasm

medium for chemical reaction

Describe the functions of the ; Cell Membrane

Regulates the movement of substances into and out of the cell.

Describe the functions of the ; cell wall

Supports cells and prevents them from changing shape

Describe the functions of the ; mitochondria

The site of aerobic respiration where ATP is produced.

Describe the functions of the ; chloroplasts

The site where photosynthesis takes place. Some parts of photosynthesis happen in the grana, and other parts happen in the stroma. ( a thick fluid found in chloroplasts)

Describe the functions of the ; Ribosomes

The site where proteins are made

Describe the functions of the ; vacuole

Helps maintain pressure inside the cell and keep the cell rigid. This stops plants from wilting.

Also involved in the isolation of unwanted chemicals inside the cell.

Similarities and differences in the structure of plant and animals cells

Similarities (found in both):

cell membrane

nucleus

cytoplasm

ribosomes

mitochondria

\
Differences (found in only plant cells):

Cell wall

permanent vacuole

chloroplasts

TRIPLE ONLY: Explain the importance of cell differentiation in the development of specialised cells

cell differentiation is the process by which cell changes to become specialised for its job. So it can turn into any cells.

TRIPLE ONLY : Advantages of using stem cells in medicine

Great potential to treat a wide - variety of diseases from diabetes and paralysis

\
Organs developed from a patients own stem cells reduces the risk of organ rejection and the need to wait for an organ donation

\
Adult stem cells are already used successfully in a variety pf treatments acting as proof of benefits

TRIPLE ONLY : Disadvantages of using stem cells in medicine

Risks/issues

Stem cells cultured in the lab could become infected with a virus which could be transmitted to the patient

There is a risk of cultured stem cells accumulating mutations that can lead to them developing into cancer cells

Low numbers of stem cell donors

\
Social issues

It is possible for embryonic stem cells to be collected before birth (from amniotic fluid) or after birth (umbilical cord blood) and stored by a clinic - but this can be expensive and isn’t an option for everyone

A lack of peer - reviewed clinical evidence of the success of stem cell treatments

Educating the public sufficiently about what stem cells can and cannot be used for

\
Ethical issues

Stem cells may be sourced from unused embryos produced in IVF treatment

It is unethical to create embryos through therapeutic cloning and then destroy them

\

identify the chemical elements present in : carbohydrates

Carbohydrates are made up of **simple sugars**

carbon, hydrogen and oxygen

identify the chemical elements present in : Proteins

They all contain Carbon, Hydrogen, Nitrogen and Oxygen

identify the chemical elements present in : Lipids

Lipids contain Carbon, Hydrogen and Oxygen atoms

Describe the structure of : Carbohydrates

Carbohydrates are made up of Starch and Glycogen

Starch and Glycogen are made up of Simple sugars

\

Describe the structure of : Proteins

Amino acid chains

Describe the structure of : Lipids

made up of glycerol and fatty acids

PRACTICAL: How to test for glucose

Preparing a food sample

* Break up the food using a pestle and mortar
* Transfer to a test tube and add distilled water
* Mix the food with the water by stirring with a glass rod
* Filter the mixture using a funnel and filter paper, collecting the solution
* Proceed with the food tests
* Add **Benedict's solution** to the sample solution in a test tube
* **Heat** in a boiling water bath for **5 minutes**
* Take the test tube out of the water bath and observe the colour
* A positive test will show a colour change from **blue to orange / brick red**

PRACTICAL:How to test for starch

* Break up the food using a pestle and mortar
* Transfer to a test tube and add distilled water
* Mix the food with the water by stirring with a glass rod
* Filter the mixture using a funnel and filter paper, collecting the solution
* Proceed with the food tests
* We can use iodine to test for the presence or absence of starch in a food sample
* Add drops of **iodine solution** to the food sample
* A positive test will show a colour change from **orange-brown to blue-black**

PRACTICAL:How to test for Protein

* Break up the food using a pestle and mortar
* Transfer to a test tube and add distilled water
* Mix the food with the water by stirring with a glass rod
* Filter the mixture using a funnel and filter paper, collecting the solution
* Proceed with the food tests
* Add drops of **Biuret solution** to the food sample
* A positive test will show a colour change from **blue to violet/purple**

PRACTICAL:How to test for Lipids

* Break up the food using a pestle and mortar
* Transfer to a test tube and add distilled water
* Mix the food with the water by stirring with a glass rod
* Filter the mixture using a funnel and filter paper, collecting the solution
* Proceed with the food tests
* Mix the food sample with **4cm3 of ethanol** and shake
* Allow time for the sample to dissolve in the ethanol
* Strain the ethanol solution into another test tube
* Add the ethanol solution to an equal volume of **cold distilled water (4cm3)**

\
* A positive test will show a **cloudy emulsion** forming

What are Enzymes

* Enzymes are proteins that act as **biological catalysts** to **speed up** the rate of a chemical reaction **without being changed** or used up in the reaction

What are enzymes reactions in a metabolic reaction

* **Step One:** Enzymes and substrates randomly move about in solution
* **Step Two:** When an enzyme and its complementary substrate randomly collide an enzyme-substrate complex forms, and the reaction occurs
* **Step Three:** A product (or products) forms from the substrate(s) which are then released from the active site. The enzyme is unchanged and will go on to catalyse further reactions

\

What is a metabolic Reaction ?

metabolic reactions are the biochemical reactions that transform food into energy in our body and its cells

How can temperature affect enzyme functions

* Enzymes work fastest at their ‘**optimum temperature**’
* In the human body, the optimum temperature is 37⁰C

\
* Heating to high temperatures (beyond the optimum) will **break the bonds** that hold the enzyme together and it will lose its shape
* This is known as **denaturation**


* Denaturation is **irreversible** - once enzymes are denatured they cannot regain their proper shape and activity will stop

PRACTICAL:Investigate how enzyme activity can be affected by changes in temperature

* Add 5cm3 starch solution to a test tube and heat to a set temperature using beaker of water with a Bunsen burner
* Add a drop of **Iodine** to each of the wells of a spotting tile
* Use a syringe to add 2cm3 **amylase** to the starch solution and mix well
* Every minute, transfer a droplet of solution to a new well of iodine solution (which should turn blue-black)
* Repeat this transfer process until the iodine solution **stops turning blue-black** (this means the amylase has broken down all the starch)
* Record the time taken for the reaction to be completed
* Repeat the investigation for a range of temperatures (from 20°C to 60°C)

\
\

how can enzyme function can be affected by changes in Ph altering the active site

* If the **pH is too high or too low**, the **bonds** that hold the amino acid chain together to make up the protein can be **disrupted/destroyed**
* This will **change the shape of the active site**, so the **substrate can no longer fit** into it, reducing the rate of activity

TRIPLE ONLY/PRACTICAL: test enzyme reaction with dif ph

* Add a drop of **iodine** to each of the wells of a spotting tile
* Use a syringe to place 2 cm3 of **amylase** into a test tube
* Add 1cm3 of **buffer solution** (at pH 2) to the test tube using a syringe
* Use another test tube to add 2 cm3 of **starch solution** to the amylase and buffer solution, start the stopwatch whilst mixing using a pipette
* Every 10 seconds, transfer a droplet of the solution to a new well of iodine solution (which should turn blue-black)
* Repeat this transfer process every 10 seconds until the iodine solution **stops turning blue-black** (this means the amylase has broken down all the starch)
* **Record the time** taken for the reaction to be completed
* Repeat the investigation with buffers at different pH values (ranging from pH 3.0 to pH 7.0) 

\

what is The process of diffusion by which substances move in and out of cells

Diffusion is the net movement of particles from an area of high concentration to an area of lower concentration

particles flow through the cell membrane, they move about randomly so travel both ways but if there is more particles on one side an overall net movement takes place

The process of Osmosis by which substances move in and out of cells

Osmosis is the net movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration

The process of Active Transport by which substances move in and out of cells

Active Transport is the movement or particles against a concentration gradient from an area of lower concentration to an area of higher concentration using energy which is released during respiration

How does the surface area to volume ratio affect movement in and out of cells

* The **bigger** a cell or structure is, the **smaller its surface area to volume ratio** is, slowing down the rate at which substances can move across its surface

How does the distance affect movement in and out of cells

* The **smaller the distance** molecules have to travel the **faster** transport will occur

extra info

* This is why blood capillaries and alveoli have walls which are only one cell thick, ensure the rate of diffusion across them is as fast as possible

\
\

How does the temperature affect movement in and out of cells

* The **higher** the temperature, the **faster** molecules move as they have more energy

why
* This results in more collisions against the cell membrane and therefore a faster rate of movement across them

How does the concentration gradient affect movement in and out of cells

* The **greater the difference** in concentration on either side of the membrane, the **faster** movement across it will occur

why
* This is because on the side with the higher concentration, more random collisions against the membrane will occur

PRACTICAL: investigate diffusion and osmosis using living and non living systems

* Using a knife, cut 2 **equally-sized** cubes of beetroot
* The pieces must have the same dimensions so that they all have **equal surface areas and volumes**, as these factors could affect the rate at which the pigment leaks out

\

\
* **Rinse** the beetroot pieces
* To **remove** any pigment released during cutting

\
* Put 5 cm3 of water into 2 test tubes labelled A and B
* Keep test tube A at **room temperature** and transfer test tube B to a **hot water bath at 90℃**
* Leave the test tubes for 2 minutes, then add a piece of beetroot into each test tube
* After 10 minutes, **observe the colour of the liquid** in both test tubes
* You should notice that at the **higher temperature**, **more of the pigment has leaked out** of the beetroot

What is the process of photosynthesis

* Photosynthesis is an endothermic reaction in which energy from sunlight is transferred to the chloroplasts in green plants
* Energy from sunlight is **absorbed by chlorophyll**, a green pigment found inside chloroplasts
* Green plants use this energy to make the carbohydrate **glucose** from the raw materials **carbon dioxide** and **water**
* At the same time, **oxygen** is made and released as a waste product

photosynthesis word equation

carbon dioxide + water → glucose + oxygen

photosynthesis balanced symbol equation

6CO2 + 6H2O →light → C6H12O6 + 6O2

how does carbon dioxide concentration affect the rate of photosynthesis

* This means the **more carbon dioxide** that is present, the **faster the reaction** can occur

how does light intensity affect the rate of photosynthesis

* The **intensity** of the light available to the plant will affect the amount of energy that it has to carry out photosynthesis
* The **more** **light** a plant receives, the **faster** the rate of photosynthesis

how does temperature affect the rate of photosynthesis

* As temperature increases the number of collisions increases, therefore the rate of photosynthesis increases
* However At higher temperatures, enzymes that control the processes of photosynthesis can be **denatured**

– this reduces the overall rate of photosynthesis

\
\

Describe the structure of the leaf and explain how it is adapted for photosynthesis

the top layer is the upper epidermis

the palisade mesophyll tissue

spongy mesophyll tissue

lower epidermis

guard cells

vascular bundle (xylem and phloem)

chloroplasts

\
air space

describe the upper epidermis

thin and transparent to allow light to enter palisade mesophyll layer underneath it

describe the waxy cuticle

the protective layer on top of the leaf, prevents water from evaporating

Describe the palisade mesophyll

column-shaped cells tightly packed with chloroplasts to absorb more light, maximising photosynthesis

describe the spongy mesophyll

contains internal air spaces that increase the surface the surface area to volume ratio for the diffusion of the gases mainly carbon dioxide

describe the lower epidermis

contains guard cells and stomata

describe the guard cells

absorbs and loses water to open and close the stomata to allow carbon dioxide to diffuse in oxygen to difuse out

describe the stomata

where the gas exchange takes place; opens during the day, and closes during the night. Evaporation of water also takes place from here. In most plants, found in much greater concentration on the underside of the leaf to reduce water loss.

Describe the vascular bundle

contains xylem and phloem to transport substances to and from the leaf

describe the xylem

transports water into the leaf for mesophyll cells to use in photosynthesis and for transpiration from stomata

describe to phloem

transports sucrose and amino acids around the plant

why do plants require mineral ions for growth

* Photosynthesis provides a source of carbohydrates, but plants contain and require many other types of biological molecule; such as proteins, lipids and nucleic acid (DNA)

What’s the function of magnesium in plants

magnesium is needed to make chlorophyll, a deficiency of magnesium causes yellowing between the veins of the leaves

What’s the function of nitrates in plants

nitrates are a source of nitrogen needed to make amino acids **to build proteins,** a deficiency causes stunted growth and yellowing of leaves

PRACTICAL: Investigate photosynthesis, showing the evolution of oxygen from a water plant, the production of starch and the requirements of light, carbon dioxide and chlorophyll

* **Destarch** the plant by placing it in a dark cupboard for 24 hours
* This ensures that **any starch already present in the leaves will be used up** and will not affect the results of the experiment
* Following de-starching, **partially cover a leaf of the plant with aluminium foil** and place the plant in sunlight for a day
* Remove the covered leaf and test for starch using iodine using the method below

\
* Drop the leaf in **boiling water**
* This **kills the tissue and breaks down the cell walls**
* Transfer the leaf into hot **ethano**l in a boiling tube for 5-10 minutes
* This **removes the chlorophyll** so colour changes from iodine can be seen more clearly
* Dip the leaf in boiling water
* This is done to soften the leaf tissue after being in ethanol
* Spread the leaf out on a white tile and cover it with **iodine solution**

\

what are the sections in a diet (7)

1. **Carbohydrates**
2. **Proteins**
3. **Lipids**
4. **Dietary Fibre**
5. **Vitamins**
6. **Minerals (mineral ions)**
7. **Water**

what is the function and source of carbohydrates

source of energy, bread, cereals, pasta, rice, potatoes

what is the function and source of protein

growth and repair of muscles, meat, fish, eggs, pulses, nuts

what is the function and source of lipids

insulation and energy storage, butter, oil, nuts

what is the function and source of dietary fibre

provides bulk (roughage) for the intestine to push food through it, vegetables, whole grains

what is the function and source of vitamins

needed in small quantities to maintain health, fruits and vegetables

what is the function and source of minerals

needed in small quantaties to maintain health, fruits and vegetables, meats, dairy products

what is the function and source of water

needed for chemical reactions to take place in cells, water, juice, milk, fruits and vegetables

what is the function and source of Calcium

Needed for strong teeth and bones and is involved in the clotting of blood. Deficiency can lead to osteoporosis later in life.

Milk, cheese, eggs

what is the function and source of Vitamin D

Helps the body to absorb calcium and so required for strong bones and teeth.

Oily fish, dairy products, also made naturally by the body in sulight

what is the function and source of Vitamin C

Forms an essential part of collagen protein, which makes up skin, hair, gums and bones.

Deficiency causes scurvy

Citrus fruit, strawberries, green , vegetables

what is the function and source of Vitamin A

Needed to make the pigment in the retina for vision

Meat, liver, dairy, leafy green vegetables like spinach, eggs

what is the function and source of Iron

Needed to make haemoglobin, the pigment in red blood cells that transports oxygen

red mat

why are the Dietary needs dependent on age

The amount of energy that young people need increases towards adulthood as this energy is needed for growth. Children need a higher proportion of protein in their diet than adults as this is required for growth. Energy needs of adults decreases as they age.

Dietary requirements depending on activity levels

The more active, the more energy is required for movement as muscles are contracting more