OCR 21 st Century Science Unit B4a Revision

OCR 21st Century Science Unit B4a Revision

Animal and Plant cellsRespiration and Photosynthesis

mitochondria contain enzymes for the reactions in aerobic respiration (in animals, plants and yeast)

cell membrane allows gases and water to pass in and out of the cell freely while presenting a barrier to other chemicals

nucleus or circular DNA in bacteria contains DNA which carries the genetic code for making enzymes used in the chemical reactions of respiration

cytoplasm where enzymes and proteins are made

chloroplasts contain chlorophyll and the enzymes for the reactions in photosynthesis

Animal and Plant Cells

Respiration

Animals and plants have many uses for the energy they generate from respiration:

1)To perform the life processes, such as moving, _____ etc

2)To build up body _______

3)To maintain a constant body ___________ (warm-blooded mammals only)

4)To build up sugars, ________ and other nutrients in plants

5)Active __________

Words – nitrates, tissue, proteins, transport, growing

Uses for respiration summary

1) Glucose (sugar) can be used to make long chains of insoluble starch…

Glucose molecules

Starch molecule

“Synthesis” means “making large molecules out of small ones”. Two examples:

2) Glucose can be combined with nitrates to make proteins (for growth)…Glucose

molecules Proteins

Synthesis

• all living things depend on chemical reactions within cells that require energy released by respiration

• Respiration is a series of chemical reactions that release energy by breaking down large food molecules in all living cells

Aerobic Respiration

glucose + oxygen

carbon dioxide + water (+ energy released)

C6H12O6 + 6O2 6CO2 + 6H2O

All living organisms have to move, _____, reproduce etc. Each of these life processes needs ENERGY. ___________ is the process our bodies use to produce this energy:

Glucose + oxygen water + carbon dioxide + ENERGY

The glucose we need comes from ______ and the oxygen from _________. Water and carbon dioxide are breathed out. The MAIN product of this equation is _________. Respiration happens in _________ in cells.

Words – breathing, energy, grow, respiration, food, mitochondria

Aerobic respiration summary

anaerobic respiration takes place in animal, plant and some microbial cells in conditions of low oxygen or absence of oxygen, to include:

Anaerobic Respiration

In Animal Cells:

glucose lactic acid (+ energy released)

In Yeast

glucose ethanol + carbon dioxide (+ energy released)

Happens in roots in waterlogged soil bacteria in puncture wounds human cells during vigorous exercise

Unlike aerobic respiration, anaerobic respiration is when energy is provided WITHOUT needing _________:

Glucose lactic acid + a bit of energy

This happens when the body can’t provide oxygen quick enough for __________ respiration to take place.

Anaerobic respiration produces energy much _______ than aerobic respiration but only produces 1/20th as much.

Anaerobic respiration can also take place in other low-oxygen conditions, such as plant roots in _________ soil or bacteria in ________ wounds.

Words – oxygen, aerobic, quicker, puncture, waterlogged

Anaerobic respiration summary

4)

2)

Mitochondria – contain enzymes for respiration reactions

Cell Membrane – controls what comes in and out

Cytoplasm - where enzymes are made

Nucleus – carries genetic info for making enzymes

1)

3)

In bacteria cells, this job is done by circular DNA

Respiration in cells

OCR 21st Century Science Unit B4b Revision

Enzymes, Osmosis and Diffusion

Enzymes in respiration and photosynthesis

Enzymes are proteins that speed up chemical uses. Here are two important natural uses for them:

Cells use glucose to generate energy – this process is called “respiration”. Respiration happens in mitochodria and is catalysed by enzymes.

Photosynthesis is catalysed by enzymes in the cells.

Enzymes- The lock and KeyModel

• enzymes are proteins that speed up chemical reactions

• cells make enzymes according to the instructions carried in genes

• molecules have to be the correct shape to fit into the active site of the enzyme (the lock and key model)

Enzyme Substrate

Factors affecting enzyme action (Denaturing)

• The shape of the enzyme is vital to its function.• The main factors affecting enzyme action are 1.) temperature and 2.) pH

1.) High temperatures can destroy the enzymes ‘special shape’ so it becomes denatured.

2.) Different enzymes work best at different pH values.

normal

heat

pH

denatured

Optimum conditions

Enzymes are denatured

beyond 40OC

Enzymes work best in certain conditions:

Enzyme activity

Temp pH pH400C

Could be protease (found in the stomach)

Could be amylase (found in the intestine)

Enzymes are used in industry to bring about reactions at normal temperatures and pressures that would otherwise be expensive. However, most enzymes are denatured at high temperatures and can be costly to produce.

Diffusion and concentration gradients

• This results in a net movement from a region where they are of a higher concentration to a region of lower concentration

highconcentration

lowconcentration

• Diffusion is the spreading of the particles of a gas, or of any substance in solution.

•The greater the difference in concentration, the faster the rate of diffusion.

Diffusion Summary

Diffusion is when particles spread from an area of high concentration to an area of ___ concentration. The particles move along a “concentration _____” and this process takes no _____ (it’s a “passive” process”). Diffusion can be accelerated by increasing the _______ of the particles, which makes them move _______.

Words – faster, low, gradient, temperature, energy

Osmosis

Osmosis

Osmosis summary

Osmosis is a “special kind of ___________”. It’s when water diffuses from a __________ area to a less concentrated area through a partially permeable _________ (i.e. one that allows water to move through but not anything else):

In this example the water molecules will move from left to right (along the concentration ______) and gradually _____ the sugar solution. Plants use osmosis to take in water through their roots.

Words – membrane, concentrated, dilute,

diffusion, gradientWater

Whic

h w

ay d

oes

movem

en

t ta

ke p

lace

?Strong sugar

solution

Medium sugar

solution

Weak sugar solution

Pota

to c

ells

Active transport

Active transport summary

In diffusion substances moved along a concentration gradient. In active transport, substances move against this gradient:

This process takes ______ and this comes from ___________. It enables cells to take in substances even though there are in very small __________. Root hair cells take in ______ using active transport.

Words – concentration, energy, respiration, nutrients

Outside cell

Inside cell

Cell membrane


Animal & Plant cells and Stem cells

Specialisation of animal cells

White blood cell

Egg cell (ovum)

Ciliated epithelial cell

Nerve cell (neurone)

During the development of a multi-celled organism cells differentiate to form specialised cells:

1. Guard cell – can open and close to control exchange of gases

and water loss

2. Sperm cell – long tail providing movement s it can swim to and fertilise egg. Nucleus contains

genetic material

3. Red blood cell – concave disc shape -

increases area to carry more oxygen

6. White blood cell – can

change shape to digest microbes

5. Root hair cell – large surface area to absorb water and minerals. Thin cell wall so minerals can pass through easily.

Positioned close to xylem tissue.

4. Egg cell (ovum) – large –

maximum exposure for sperm, has a

large food store

7. Neurone – long like

wires to carry messages around the

body

Cells, tissues and organs Basically, all living things are made up of cells…

A group of CELLS makes up a TISSUE

A group of TISSUES makes up an ORGAN

A group of ORGANS makes up a SYSTEM

A group of SYSTEMS make up an ORGANISM

Adult stem cells

White blood cell

Egg cell (ovum)

Ciliated epithelial cell

Nerve cell (neurone)

It is also possible to have adult stem cells – these are unspecialised cells that can become specialised later (but they can’t form ALL types of cell)

Adult stem cells can be found in places like bone marrow.

Adult stem CellsCells inside an organism contain the same genes. So how can cells specialise if they have the same genes and make the same proteins?

The reason is that many of the genes in the nucleus are “switched off” so that the cell only produces the proteins it needs.

It is possible to “switch on” different genes to make the cell produce different proteins – this is the basis of stem cell research.

Adult Stem cellsAs well as adult stem cells from bone marrow, stem cells can also come from...

Egg and sperm

Embryo

Cloned embryos

These stem cells have the potential to develop into any kind of cell. The rest of the embryo is destroyed. Most of these embryos come from unused IVF treatments.

The ethical issue:

Should these embryos be treated as humans?

Meristems

Plant growth occurs in areas called meristems. These meristems are “mitotically active”:

Cells from the meristem behave like stem cells – they can develop into any kind of cell. Cloned plants can be produced from these cells.

This meristem causes the plant to grow upwards.

This meristem causes the plant to grow in width.

Phototropism…………………………………………

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Plant hormones The growth of roots and shoots is controlled by hormones:

In the roots hormones slow down growth of the cells in the lower region, which makes the root bend down.

In the shoots the hormone auxin is “destroyed” by light, so the shoot will bend towards the light as the cells on the shaded side grow quickest.

Shoots grow towards light (positive phototropism) and against gravity (negative geotropism).

Roots grow away from light (negative phototropism) and in the direction of gravity (positive geotropism).

Phototropism summary

Cuttings …………………………………………

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DNA and Mitosis & Meiois

Inside the nucleus

the genetic code is in the cell nucleus of animal and plant cells but proteins are produced in the cell cytoplasm

DNA• DNA has a double helix

structure• both strands of the DNA

molecule are made up of four different bases which always

• pair up in the same way: A with T, and C with G

• the order of bases in a gene is the genetic code for the production of a protein

DNA and coding for proteins

• the order of bases in a gene is the code for building up amino acids in the correct order to make a particular protein

1) DNA “unravels” and a copy of one strand is made

2) The strand copy is made to produce RNA

3) The copy (with its code) then moves towards the ribosome

4) The ribosome “decodes” the code which tells the ribosome how to make the protein

In other words, genes do NOT leave the nucleus but a copy of the gene (the mRNA) carries the genetic code to the cytoplasm.

Building proteins

Building proteins ………………………………………………………………

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DNA summary

Some facts:

- DNA has a “double ______” structure

- This contains instructions on what a cell does, how the organism should work etc

- The instructions are in the form of a ______

- The code is made up from the four ____ that hold the strands together with hydrogen bonds; A always pairs with T and C with G

- The bases represent the order in which _____ acids are assembled to make specific ________

Words – helix, amino, code, bases, proteins

Chromosomes in body cells

• In body cells the chromosomes are in pairs

• Body cells have two sets of chromosomes;

• Sex cells (gametes) have only one set.• Sex cells (gametes) are made by

meiosis

Asexual and sexual reproduction

• cell division by mitosis produces two new cells that are genetically identical to each other and to the parent cell

• a fertilised egg cell (zygote) divides by mitosis to form an embryo

parent cell

mitosis

daughter cells

Mitosis

Each daughter cell has the same number of chromosomes and

genetic information as the parent – it’s a

“clone”.

The chromosomes are copied…

The chromosomes separate…

The nucleus divides…

Mitosis

Mitosis summary

• meiosis is a type of cell division that produces gametes• in meiosis, it is important that the cells produced only

contain half the chromosome number of the parent cell• a zygote contains a set of chromosomes from each

parent.

Meiosis

Each daughter cell has half the number of

chromosomes of the parent.

Meiosis

Meiosis summary

Mitosis:

1. Used for growth and repair of cells

2. Used in asexual reproduction

3. Cells with identical number of chromosomes and genetic information are produced (“clones”)

Meiosis:

1. Used to produce haploid gametes for sexual reproduction

2. Each daughter cell has half the number of chromosomes of the parent

Mitosis Vs Meiosis


Nervous system and Reflex actions

The nerve cell

The CENTRAL NERVOUS SYSTEM (CNS) enables us to react to changes in our surroundings (“stimuli”). It consists mainly of the brain, the spinal chord, nerve cells (“neurones”) and receptors.

Receptor cells Types of receptor:

1) Light receptors in the eyes

2) Sound receptors in the ears

3) Taste receptors on the tongue

4) Smell receptors in the nose

5) Touch, pressure and temperature receptors in the skin

6) Changes of position receptors in the ears (balance)

The nerve cell

NucleusMuscle strands

(effector)

Axon – a long extension of cytoplasm

surrounded by a membrane

Nerve cells (neurons) are elongated with branched endings to connect to many muscles fibres and aid the transmission of electrical impulses:

Fatty sheath to increase the speed of transmission and to insulate the

neuron from surrounding cells

CNS and PNS

There are two types of neurone we need to consider:

The Central Nervous System (CNS) is the spinal cord and brain:

The Peripheral Nervous System (PNS) is the collection of neurones connected to the CNS:

2) Motor neurone

Impulse

These carry impulses from the CNS to effectors

1) Sensory neurone

Impulse

These carry impulses from the receptors to the CNS

Synapse summary

Neurones never ____ each other – there is a small gap between them called a _____. A signal is sent from one _______ to the next by a _______ transmitter across the synapse (called a “neurotransmitter”). These transmitters are then ________ back into the sensory neurone to be used again. This process only reacts with specific chemicals that bind to the receptor molecules.

Words – chemical, synapse, neurone, touch, reabsorbed

A conscious action is one where the brain makes a considered response. Here’s what happens:

Stimulus Receptor Sensory Neurone Coordinator

Motor Neurone Effector Response

1) Receptors in your skin detect a stimulus

3) Here another sensory neurone carries the signal to the brain

4) The brain decides to move away the hand

5) This impulse is sent by MOTOR NEURONES to the hand muscles (the effectors) via the spinal chord…

2) The impulse is carried by SENSORY NEURONES to the spinal chord

6) Which then moves the hand away

A Conscious action

A conscious nervous pathway…………………………………………

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Copy and complete

3 types of neurons

The reflex arc …………………………………………

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Simple reflexes

Babies can demonstrate simple reflexes:

1)Stepping reflex (legs step back if you hold the baby up)

2)Startle (or moro) reflex (when a baby hears a loud noise it spreads its arms and legs out)

3)Grasping reflex (gripping your finger with their hands)

4)Rooting reflex

5)Sucking reflex (for breast feeding)

Summary


Learning and memory

Drugs and the nervous systemDrugs are classed as “a substance that affects the central nervous system, causing changes in psychological behaviour and possibly addiction”. They do this by affecting the transmission of impulses. Consider Ecstasy for example:

Ecstasy (MDMA) blocks the sites in the brain’s synapses where the

transmitter substance serotonin is removed.

Beta blockers and Prozac can also affect the transmission of impulses.

Some drugs stop the impulse from passing across the ………………………

Drugs such as strychnine cause all the muscles in the body to go into a continuous spasm of contraction. This also stops the person from ……………………….Serotonin is a chemical released in the brain that gives feelings of pleasure. Lack of this chemical can lead to feelings of ……………………….Prozac is an ……………………… ……………drug that causes serotonin concentration to build up in synapses. The Prozac molecule blocks the re-uptake of serotonin from a synapse.Beta blockers are drugs that can help people who suffer from angina (chest pain due to a ……………………… condition). They work by blocking the receptor sites on heart muscle cells so impulses from nerves which would speed up the heart are ……………………… from passing to the heart.

WORDS: synapse. Breathing depression anti-depressant heart prevented

Drugs and the nervous system summary

The cerebral cortex

The cerebral cortex is the part of our brain most concerned with intelligence, memory and consciousness. By studying the effects (e.g. memory/sight loss) when different parts of the brain are damaged scientists have been able to identify which parts of the brain control which functions.

EEG and MRI1) An electroencephalogram (EEG) is a visual record of the electrical activity generated by neurons in the brain. It works by amplifying and detecting the electrical signals from the brain.

2) Magnetic resonance imaging (MRI) scanning is a new technique that produces images of different cross sections of the brain and uses colours to represent activity.

Conditioning- Pavlov’s dogs

Ivan Pavlov, 1849-1936

I won the Nobel Prize in 1904 and am most famous for investigating “conditioned responses”:

1) Steak + dog = saliva

2) Steak + bell + dog = saliva

3) Bell + dog = salivaNotice that the final response (saliva) has no direct relation to the stimulus (the bell). Conditioned reflexes can increase an animal’s chance of survival!

Bird finds a black caterpillar and tastes it. It tastes good so it is eaten

Bird finds a black and orange caterpillar and tastes it. It is poisonous and tastes bad so it is not eaten

Bird finds a black and orange caterpillar and tastes it. It is poisonous and tastes bad so it is not eaten

Bird finds a black and orange caterpillar but avoids it because it is poisonous

Bird finds a hairy black and orange caterpillar, this one is harmless but the bird still avoids it.

Underline the primary stimulusCircle the secondary stimulusPut a box round the conditioned response

Extension: Answer the following questions in your exercise book:1. Which organisms benefit? For each one explain

how.2. Which caterpillar would you expect to find in

the highest numbers? Explain your answer.

Complex behaviour

When the brain is asked to do certain tasks different areas are “activated”. New experiences cause new neuron pathways to develop, while pathways that are not used are eventually destroyed. This is why we become better at certain tasks when we practice them more often.

PET scan showing areas “activated” by doing algebra.

Memory

Our memory is divided into two types: short term and long term.Short-term memory lasts for about 30 seconds. This is why, when you look up a new telephone number, by the time the call has ended you have forgotten the number. If more information arrives than can be held in the short-term memory then some is lost (forgotten).Long-term memory may last the whole of your life. When you sing the words of a favourite song, you are using your long-term memory. Although we often complain about how hard it is to learn new things, there is no limit to how much information you can store in your long-term memory.

Ways of improving short term memory, e.g. a phone number

Ways of improving long term memorye.g. exam revision

Multistore model Scientists have produced models to help explain how memory works. So far, none of these models has provided an exact explanation.The multistore memory model can be used to help explain some steps involved in long-term and short-term memory.

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OCR 21 st Century Science Unit B4a Revision