B4 B5 B6 Revision B4 The Processes of life B6 Growth and Development B6 Brain and Mind B4 The Processes of life Features of all living things Movement All living things are made Respiration up of cells. Sensitivity Growth Reproduction Excretion Food Enzymes Enzymes are proteins that speed up chemical reactions in cells. They need a specific constant temperature to work at their optimum. Enzymes become denatured (stop working) above about 55oC. Most enzymes work best at about 40oC. 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. lock and key active site click to react enzyme molecule 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 oxygen Chlorophyll absorbs light and uses the energy to kick-start photosynthesis Glucose 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 = eg oxygen 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 Osmosis is the same as diffusion but applies to water molecules passing through a partially permeable membrane. partially permeable membrane = starch = water movement of water molecules Low concentration of starch High concentration of starch High concentration of water Low concentration of water Starch molecules cannot pass through the partially permeable membrane but water molecules can. cell Osmosis in plant cells If too much water passes into a cell by osmosis then it may rupture. potato chip low salt concentration the potato chip absorbs water and expands high salt concentration the potato chip loses water and shrinks Molecules like glucose are moved by active transport. 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 repair Anaerobic 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   B4 Homeostasis B5 Growth and Development B6 Brain and Mind B5 Growth and Development Cytoplasm – where proteins are made Nucleus – where the genes are located DNA has a double helix structure The base pairs always pair up the same way A to T and G to C adenine Each gene codes for a specific protein nucleus cytoplasm G- C g e n e A- T T- A A- T C- G A- T AThe The copy mRNA DNA mRNA of zips unzips the travels is code used upto again to is expose to made the produce cytoplasm the using acode protein RNA (using ribosomes) This is the simplest amino acid - valine Protein is made up of amino acids joined together in chains The order of bases in a gene determines the order of amino acids that make a particular protein. The order of amino acids determines the 3D structure of a particular protein. The 3D structure of a protein determines its function (job) Cell division Mitosis involves copying the chromosomes exactly Cell division by mitosis produces two new cells identical to each other and to the parent cell 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 A zygote divides by mitosis to form an embryo 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 X The antibodies help to kill the foreign cell foreign cell with antigen White blood cells recognise it as a foreign cell and make antibodies 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. 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. plant stem A 4 D C   16    DNA cytoplasm mRNA amino acids B4 Homeostasis B5 Growth and Development B6 Brain and Mind Brain and Mind What are we sensitive to ? • light • sound • pressure • chemicals • temperature • orientation The 5 senses are: • sight eye • hearing ear • touch skin • taste nose & tongue • smell nose The retina contains light sensitive cells The lens refracts the light to focus on the retina The retina contains cells called cones which enable colour vision The Ear semi-circular canals which sense orientation The Tongue The tongue has receptors which are sensitive to chemicals and enable us to taste 4 types of flavours. The Nose The nose has receptors which are sensitive to chemicals and enable us to smell and taste. The Skin The skin has receptors that are sensitive to touch, pressure and temperature changes. How the nervous system works nerve cell neurotransmitter receptor site axon dendrite synapse acetylcholine The 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. Sequence stimulus is detected by a receptor nerve impulse travels along a sensory neurone neurotransmitter diffuses across a synapse nerve impulse travels along a relay neurone nerve impulse travels along a neurone to the brain neurotransmitter diffuses across a synapse nerve impulse travels along a motor neurone muscle contracts / hormone is released from a gland Conscious awareness of the stimulus at the same time stimulus receptor sensory neurone (nerve) central nervous system (brain and spinal cord) motor neurone (nerve) effector (muscle or gland) nervous systems use electrical impulses Fast and short lived responses Glands in the body melanin ADH ACTH, FSH, LH, growth H thyroxine PTH Involved in producing T cells adrenaline Insulin, glucagon oestrogen, progesterone testosterone Hormonal control Control of blood sugar High blood sugar level Low blood sugar level insulin released from the pancreas glucagon released from the pancreas decrease in blood sugar level increase in blood sugar level homeostasis Hormones are chemicals which travel in the blood slow and long lasting How can reflex actions be an advantage for survival ? 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 caterpillars have a poisonous toxin in their skin. Some birds develop a learned conditioned reflex or have an evolved reflex to avoid eating particular caterpillars on the basis of their colours. Simple animals rely on reflex actions for the majority of their behaviour This is a reflex response to move towards lighter areas This is a unicellular organism which needs light to survive, eg plankton This is a reflex response to something moving Woodlouse Light & dry Dark & dry Dark & moist Light & moist 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. How the brain works in a nut shell ! Microscope slide of neurons in the brain Neurotransmitters [you don’t have to know the structures] dopamine Central nervous system seratonin melatonin Peripheral nervous system acetylcholine adrenaline / epinephrine reasoning spatial sense visual cerebral cortex movement auditory, speech essential functions The cerebral cortex is the part of our brain most concerned with intelligence, memory, language and consciousness. A variety of methods can be used to map the brain CT scanner MRI scanner CT and MRI scanners can be used to get images of structures. PET scanners can be used to monitor activity in the brain PET scanner Electrical stimulation of the brain can be used in studies 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. Click 1 then 2 then 3 then 4 1 The second set of nerve cells are not stimulated enough to fire 2 One of the nerve cells in the second set receives enough input to fire 3 One 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 stem 4 The neuronal pathway doesn’t need the extra input to work Brain stem 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. 9/20 x 100   involuntary A B E C     B4 Homeostasis B5 Growth and Development B6 Brain and Mind