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B4 B5 B6 RevisionB4 B5 B6 Revision
B4 The Processes of life
B6 Growth and Development
B6 Brain and Mind
Features of all living things
Movement
Respiration
Sensitivity
Growth
Reproduction
Excretion
Food
All living things are made
up of cells.
Enzymes are proteins that speed up chemical reactions in cells.
They need a specific constant temperature to work at their optimum.
Enzymes
Enzymes become denatured (stop working) above about 55oC.
The higher the temperature the faster molecules move around and therefore (a) collide more frequently and (b) collide with more energy.
This results in an increased rate of reaction.
click to react
lock and key
enzyme molecule
Most enzymes work best at about 40oC.
active site
The active site can be changed by heating above a certain temperature and altering the pH, so that the molecules can no longer fit and the reaction cannot happen.
Enzymes at work in plants
Photosynthesis equation (takes place in chloroplasts)
light energy
6CO2 + 6H2O C6H12O6 + 6O2
chlorophyll
Carbon dioxide water glucose oxygenChlorophyll absorbs light and uses the energy to kick-start
photosynthesisGlucose is used by plant cells in 3 ways
1. Making other chemicals needed for cell growth
2. Storing energy in starch molecules
3. Releasing energy in respiration
Diffusion (passive transport)
This is the movement of molecules from a region of their high concentration to a region of their lower concentration
Region of high concentration
Region of low concentration
Diffusion causes the molecules to become evenly distributed due to their random movement.
It is like as if the molecules have moved from the region of high concentration to the region of low concentration.
Diffusion in the leaf happens through the stomata- carbon dioxide in and oxygen out
= eg oxygen
Osmosis is the same as diffusion but applies to water molecules passing through a partially permeable membrane.
= starch
= water
High concentration of starch
Low concentration of starch
partially permeable membrane
High concentration of water
Low concentration of water
movement of water molecules Starch molecules cannot pass through the partially permeable membrane but water molecules can.
If too much water passes into a cell by osmosis then it may rupture.
Molecules like glucose are moved by active transport.
cell
low salt concentration
high salt concentration
potato chip
the potato chip absorbs water and expands
the potato chip loses water and shrinks
Osmosis in plant cells
Minerals from the soil
Plants take in nitrogen from the soil as nitrate ions, they
are absorbed by root hair cells.
The cells use a process called active transport to pump
nitrates from the soil and into the roots against their
diffusion gradient.
The rate of photosynthesis
Increasing the amount of light a plant receives increases
the rate of photosynthesis up to a point.
Increasing the light intensity stops having an effect on the
rate of photosynthesis because one of the other factors e.g.
carbon dioxide, water, chlorophyll or temperature is in
short supply. This factor is called the LIMITING FACTOR
Environments and adaptations
A habitat is a place where an organism lives.
A quadrat is used to survey the plants in a
square metre.
The positioning of a quadrat in the area being
investigated is random.
Samples can be taken at regular intervals along
a straight line called a transect.
Energy for life
Aerobic respiration
Glucose + oxygen carbon dioxide + water (+ energy released)
C6H12O6 + 6O2 6CO2 + 6H2O
What happens to the energy from respiration?
• used in active transport
•movement
•building molecules used for growth and repairAnaerobic respiration
Glucose lactic acid (+energy released) – in animals
Glucose ethanol + carbon dioxide (+ energy released)
– in plants and microorganisms
Useful products from respiration
Bioethanol (used to fuel car engines) is made from
sugars in plant material.
Yeast cells take sugars and convert them into ethanol
during the process of anaerobic respiration, this is called
fermentation. Biogas is a fuel obtained from animal manure or human
waste using bacteria, it produces methane gas.
The fuel can be used to heat buildings and run
electricity generators
DNA has a double helix structure
Cytoplasm – where proteins are made
Nucleus – where the genes are located
The base pairs always pair up the same way A to T and G to C
adenine
C
T
A
T
G
T
G-
A-
T-
A-
C-
A-
C
T
A
T
G
T
nucleus cytoplasm
The DNA unzips to expose the codeA copy of the code is made using RNAThe mRNA travels to the cytoplasm The DNA zips up againThe mRNA is used to produce a protein
Each gene codes for a specific protein
gene
(using ribosomes)
The order of bases in a gene determines the order of amino acids that make a particular protein.
This is the simplest amino acid - valine
Protein is made up of amino acids joined together in chains
The order of amino acids determines the 3D structure of a particular protein.
The 3D structure of a protein determines its function (job)
Meiosis is a type of cell division that produces gametes, ie sperm and egg cells.
Cells produced by meiosis only contain half the chromosome number of the parent cell
Cell division by mitosis produces two new cells identical to each other and to the parent cell
Cell division
Mitosis involves copying the chromosomes exactly
In a human embryo, up to the eight cell stage, all the cells are identical and could produce any sort of cell required by the organism (embryonic stem cells);
After this point the cells become specialised and form different types of tissue.
Adult and embryonic stem cells have the potential to produce cells needed to replace damaged tissues.
In carefully controlled conditions of mammalian cloning, it is possible to reactivate inactive genes in the nucleus of a body cell to form cells of all tissue types.
Making stem cells using the DNA from a patient means the cells wont be rejected when they are transplanted into the patient
This means that the patient’s immune system wont attack the transplanted stem cells
foreign cell with antigen
White blood cells recognise it as a foreign cell and make antibodies
The antibodies help to kill the
foreign cell
X
With this technique the white blood cells do not recognise the
transplanted stem cells as foreign and therefore don’t attack them
New cells in plants specialise into cells of roots, leaves or flowers.
Some plant cells remain unspecialized and can develop into any type of plant cell, unlike animal cells.
Most plants continue to grow in height and width throughout their lives, unlike animals.
Plant meristems divide to produce cells that result in increased height, length of roots, and girth of the plant. If the hormonal conditions in their environment are changed, unspecialised plant cells can develop into a range of other tissues
Transport vessels: xylem and phloem
Organs: leaves, roots and flowers
Cut stems from a plant can develop roots in the presence of plant hormones (auxins) and grow into a complete plant which is a clone of the parent.
shoot tip
The action of light causes auxin to move across the shoot tip from the side getting the light to the shaded side.
plant stem
This causes the cells on the shaded side to elongate which causes the stem to bend towards the light.
This helps the plant to grow towards the light which helps its survival.
The Tongue
The tongue has receptors which are sensitive to chemicals and enable us to taste 4 types of flavours.
axon
dendrite
neurotransmitter receptor site
synapseacetylcholineThe neurotransmitter diffuses across the
gap
Receptor molecules only bind to specific chemicals, initiating a nerve impulse in the motor neuron.
At the end of a sensory neuron an impulse triggers the release of chemicals into the synapse, which diffuse across and bind to receptor molecules on the membrane of a motor neuron.
stimulus is detected by a receptornerve impulse travels along a sensory neuroneneurotransmitter diffuses across a synapsenerve impulse travels along a relay neurone
neurotransmitter diffuses across a synapse
nerve impulse travels along a neurone to the brain
nerve impulse travels along a motor neuronemuscle contracts / hormone is released from a glandConscious awareness of the stimulus
Sequence
at the same time
receptor
stimulus
central nervous system (brain and spinal cord)
sensory neurone (nerve)
motor neurone (nerve)
effector (muscle or gland)
Fast and short lived responses
nervous systems use electrical impulses
melanin
ADH
ACTH, FSH, LH, growth H
thyroxine
PTH
Involved in producing T cells
adrenalineInsulin, glucagonoestrogen, progesterone
testosterone
Glands in the body
High blood sugar level
insulin released from the
pancreas
decrease in blood
sugar level
Low blood sugar level
glucagon
released from the pancrea
s
increase in blood sugar level
Control of blood sugar
homeostasis
Hormonal control
Hormones are chemicals which travel in the blood
slow and long lasting
A new born baby has a set of reflex actions, eg:
Grasping reflex: Touching a baby’s palm will cause the baby’s fingers to curl.
Sucking reflex: Putting an object in a baby’s mouth will cause the baby to suck the object .
Diving reflex: Putting a baby in water will cause the baby to hold it’s breath and move it’s arms around
Pupil reflex
When the surroundings get darker the iris relaxes causing the pupil to dilate
When the surroundings get lighter the iris contracts causing the pupil to get smaller
This reflex helps to protect the light sensitive receptors in the eye when it is too light and to get more visual information when dark.
Some birds develop a learned conditioned reflex or have an evolved reflex to avoid eating particular caterpillars on the basis of their colours.
Some caterpillars have a poisonous toxin in their skin.
This is a unicellular organism which needs light to survive, eg plankton
This is a reflex response to move towards lighter areas
Light & dry Dark & dry
Dark & moist Light & moist
Woodlouse
A reflex response to move to dark areas enables it to hide from predators
The disadvantage of these simple reflex behaviours is not being able to respond appropriately to new situations.
Eg what if a spider is waiting for the woodlouse in the dark area !
Pavlov’s dog
The final response has no direct connection to the stimulus
A reflex response to a new stimulus can be learned
The brain can modify reflexes
For example, being given a hot plate and instinctively wanting to drop it but yet holding on to it.
dopamine
seratonin melatonin
acetylcholine
adrenaline / epinephrine
Neurotransmitters
Central nervous systemPeripheral nervous system
[you don’t have to know the structures]
visual
auditory, speech
spatial sense
essential functions
movement
reasoning
cerebral cortex
The cerebral cortex is the part of our brain most concerned with intelligence, memory, language and consciousness.
CT scanner MRI scanner
PET scanner
A variety of methods can be used to map the brain
CT and MRI scanners can be used to get images of structures.PET scanners can be used to monitor activity in the brain
MDMA - ecstasy
Ecstasy blocks the re-uptake of serotonin in the synapses of the brain.
This causes an increase in the serotonin concentration which leads to mood-enhancing effects.
During development, the interaction between mammals and their environment results in neuron pathways forming in the brain.Here, neuron pathways in the visual cortex interplay with neuron pathways in the motor cortex in order to grab an object.After many attempts the neuron pathways get fine tuned to produce the responses that we intend.
Eventually we build up a vast array of efficient pathways.
Brain stem
1
2
3
4
The second set of nerve cells are not stimulated enough to fireOne of the nerve cells in the second set receives enough input to fireOne of the nerve cells in the second set receives enough input to fire and this neuronal pathway is strengthened by a nerve impulse from the brain stemThe neuronal pathway doesn’t need the extra input to work
Click 1 then 2 then 3 then 4
This gives you a very basic idea about how neuron pathways are formed
Learning is the result of experience where certain pathways in the brain will become more likely to transmit impulses than others.
This is why some skills may be learnt through repetition.
The variety of potential pathways in the brain makes it possible for animals to adapt to new situations.
There is evidence to suggest that children may only acquire some skills at a particular age, eg language development in feral children.
A feral child is one who has been brought up by wild animals from early childhood.
Memory is basically the storage and retrieval of information.
Verbal memory can be divided into short-term memory and long-term memory.
Humans are more likely to remember information if:
• they can see a pattern in it
• there is repetition of the information, especially over an extended period of time
• there is a strong stimulus associated with it, eg colour, light, smell, sound etc
By the time you have become consciously aware of the snake your brain has already set into play a series of responses.