All living things are made of cells. E.g. Trees, animals etc are made of cells
Human cells (like most animal cells) consist of:
- A Nucleus - This contains the genetic material that controls activities within the cell
- A Cytoplasm - a gel-like substance containing enzymes. This is where the majority of chemical reactions occur
- A Cell Membrane - This holds the cell together and controls what substances enter and exit the cell
- Mitochondria - Most of the reactions for respiration occur within these. Respiration releases energy which is used within the cell.
- Ribosomes - Proteins are made within these
- Cell Wall - This is made of cellulose and strengthens the cell.
- Permanent Vacuole - This contains cell sap which is a weak solution of sugar and salts
- Chloroplasts - These are where photosynthesis occurs. The contain Chlorophyll.
Ecosystems
Plant Cells (usually) contain all the the things that animal cells contain, but with a few extra things:
Some organisms are single-celled like Yeast for example. A yeast cell has a nucleus, cytoplasm, and a cell membrane which is also surrounded by a cell wall.
Some cells don't have a nucleus. Bacteria are an example of this, they are a single-celled micro-organism but do not have a nucleus. Instead the genetic material is contained within the cytoplasm.
Diffusion is the movement of particles from an area of high concentration to an area of low concentration. For example you can smell something on the other side of a room because the particles coming from that object diffuse from an area of high concentration (around the object) to an area of low concentration (around you).
Diffusion occurs within cells, substances diffuse through the cell membrane so they can be utilized within the cell. The cell membrane only lets small particles through however, so large particles such as starch have to be broken down into smaller substances like glucose before they can pass through.
An example of diffusion within cells is the movement of oxygen from the bloodstream (The area of high concentration) to the cells (an area of low concentration) for use in respiration.
With a bigger difference in concentration, the rate of diffusion is faster.
In the lungs, blood takes in oxygen from the alveolar which has a higher oxygen concentration than the blood. The circulation then takes the oxygen rich blood away and
Cell membranes
Diffusion occur at cell membranes, dissolved substances such as sugar and amino acid can move in and out of cells by diffusion.
Larger, insoluble substances such as starch, protein and fat cannot go past the cell membrane.
Particles move randomly, they move both ways but there is a net movement to one side
Specialised Cells
Palisade cells are adapted for photosynthesis
They contain a lot of chloroplasts which increases photosynthesis
They are tall so they have a lot of surface exposed for absorbing CO2 from below
They are thin so many can be fit under the upper epidermis
Guard cells are adapted to open and close pores which controls gas exchange and water loss
They are kidney shaped which opens and closes stomata in the leaf
The stomata closes when the plant has a lot of water, as they fill up with water and become turgid making the pores open for exchanging gases
When the plant is short on water, they close as they lose water and become flaccid
They have thin outer walls and thick inner walls which allow this to work
They close at night as they are also sensitive to light, this saves water.
Red blood cells are adapted to carry oxygen
They have a concave shape which increases the surface area for absorbing oxygen
They contain a lot of haemoglobin which absorbs oxygen
They have no nucleus to leave more space for haemoglobin
Sperm cell are specilised for reproduction
They have a streamlined head with a tail ehich allows it to swim faster
It contains alot of mitochondria which help provide the energy needed
They have enzymes in their head to digest through the cell membrain of he egg
When it fuses with the egg, the cell membrane of the egg changes the structure of the cell membrane with stops more sperm getting in and ensures the offspring has the right amount of DNA
Egg cells contain huge food reserves which is used to feed the embryo
Differentiation occurs during the development of a multicellular organism
It is the process where cells become specialized for a particular job
Specialised cells form tissues which forms organs which forms organ systems
Similar cells work together to form tissues
Examples are
Muscular tissues
Glandular tissues
Epithelial tissue
Organs are groups of different tissues
Organs form an organ system e.g the digestive system
Plant Structure
Plants are made of organs
These are the stems, roots and leaves, etc.
Organs are made from tissue.
Mesophyll tissues are where photosynthesis mostly occur
Xylem and Phloem transport water, mineral ions and sugar (sucrose) around the plant
Epidermal tissue covers the plant
Carbon Dioxide + water > glucose + oxygen
Photosynthesis happens in the chloroplasts of plant cells
Chloroplasts contain chlorophyll which absorbs sunlight
Photosynthesis happens in leaves
Leaves have different layers
Waxy cuticle
Upper epidermis
Palisade layer
Spongy layer
Lower epidermis
Limiting factors which affect photosynthesis
Light
Temperature
Water
Nutrient
Carbon dioxide
Greenhouses
Use of artificial light can allow photosynthesis to happen a night
Artificial heating allow photosynthesis to be at an increased rate
Additional carbon dioxide also allow photosynthesis to be at an increased rate.
These costs money but it also increases crop yield which would outweigh the cost
They would need to find the optimum condition for cost.
Paraffin lamps generates heat as well as light and carbondioxide
Glucose
Plants use glucose for many things
Respiration which releases energy which is used to convert other glucose into useful substances
Glucose can be converted to cellulose to make cell walls
Protein can be made by reacting glucose with nitrate ions absorbed from the soil
They can be stored as Starch or Fats
Starch is insoluble so it can be stored until needed
Sugar can be turned to lipids for storing in seeds
Distribution of organisms
Physical factors
Temperature
Amount of light
Availability of water
Availability of nutrients
Availability of oxygen and carbon dioxide
Environment All the conditions that surround a living organism
Habitat A place where organisms live
Population The amount of a single species in a habitat
Community The total of different organisms that live together in the habitat
Ecosystem A community and the habitat.
Transect - a line across a habitat or part of one.
Organisms are observed and recorded at regular intervals along the transect
Quadrats - a square grid, placed randomly ( gridding the area and using a random generator to find coordinates )
Proteins and Enzymes
Aminos acids fold into particular shapes to produce proteins.
Enzymes are biological catalysts.
They operate best at optimum temperatures and acidity of its surroundings.
They can denature at higher temperatures or extreme pH
There are 20 different amino acids
There are hundreds of protein molecules as amino acids join together at different sequences
Protein can act as structural components, hormones, antibodies and enzymes.
Enzymes increase the rate of chemical reactions without being used up.
They are proteins folded into complex shapes.
Substrates fit into an active site and is broken down into two.
Enzymes in the human body normally have an optimum temperature of 37 degrees.
When it goes past 37, the rate slows down as enzymes become denatured.
Optimum pH is around 7.5 (neutral) but pepsin found in the stomach's optimum pH is around 2
Amylase - Starch > Sugar - pancreas, small intestine, salivary glands,
Protease Proteins > Amino acids - pancreas, small intestine, stomach
Lipase - Fats > glycerol and fatty acids - pancreas, small intestine
Stomach acid is hydrochloric acid which kills harmful microbes.
Enzymes (pepsin) works best at an acidic pH
Bile is made in the liver and stored in the gall bladder.
It neutralises stomach acid from the stomach in the small intestine and it also makes the condition alkaline.
Enzymes work best at an alkaline pH in the small intestine.
Industry uses
Protease - predigested baby food + detergents
Lipase- Biological detergents to break down stains into soluble substances
Carbohydrase- Make sugar syrup from starch syrup.
Isomerase - Glucose syrup into fructose syrup which is sweeter and can be used in slimming as you use smaller amounts.
Respiration
Release energy by using glucose
Aerobic respiration uses oxygen
Anaerobic does not, it builds up an oxygen debt.
Aerobic respiration
Glucose + oxygen > Carbon dioxide + water
Happens in mitochondria in cells inside the cytoplasm
This reaction is controlled by enzymes.
The energy can also be used to build substances e,g, amino acids and protein.
The energy can also be used in mammals to keep body warm
Muscle cells respire more when they are exercising
Oxygen and glucose are needed more and needs to be delivered quickly.
Carbon dioxide needs to be removed quickly
Increasing the heart rate, breathing and depth of breathing allows this to happen.
This increase the rate of gas exchange in the lungs.
We can store glucose in our muscles as glycogen.
Anaerobic respiration
When we don't get enough oxygen, we use this process
This is the incomplete break down of glucose and releases around 5 % of the energy by aerobic.
This forms a waste product called lactic acid from glucose alone
Glucose > Lactic acid.
Muscles become tired after a long time of activity, they stop contracting efficiently as lactic build up form anaerobic respiration, the lactic acid can be removed by blood flow.
We oxidise lactic acid to carbon dioxide and water. As we exercise we cumilate and oxygen debt, this is the amount of oxygen needed to oxidise the lactic acid.
We continue to breath deeply and quickly after exercise as this happens
Cell division
DNA (deoxyribonucleic acid) are long and complex
They carry the genetic codes that determines the characteristics of an organism.
Identical twins have the same DNA but other people have different.
Gene is a short part of a DNA, it codes for a specific characteristic.
Chromosomes are made form long DNA molecules .
46 are found in normal animal cells' nuclei
Mitosis
Genetic material is copied,
Form X shaped chromosomes
Line up at centre
Spindle fibres pull them apart
New membrane form
Cytoplasm splits
Mitosis happens during growth and repair of normal cells.
Gametes
Sex cells
Sperm and egg.
They contain 1 set of generic information when normal cells have 2
Fertilisation occurs when a sperm fuses with an egg,
They divide by mitosis after.
Meiosis- gametes are formed from this kind of cell diviion.
Chromosomes duplicate,
pair up,
Sections of DNa swapped
Divide
Divide again
Stem cells can be differentiated to become specialised cells.
They come from embryos or adult bone marrow. This can be used to treat conditions such as parkinson's disease and paralysis. However there are social and ethical issues regarding this research
Genetic variance
Alleles are different forms of a gene.
They can be dominant or recessive.
Human body cells have 23 pair of chromosomes.
One of these pair control the inheritance of gender.
XY = male XX = female
Alleles control characteristics eg. one can be brown eyes and one can be blue eyes
Dominant alleles develop on the organism if one of both of the chromosomes are present in the pair
Recessive alleles only develop if both alleles are recessive on both chromosomes in the pair.
Heterozygous = 2 different alleles
Homozygous = 2 same alleles
Homozygous recessive = 2 same but recessive alleles.
Variation only occur at sexual reproduction but no a sexual reproduction
There are 2 possible gametes which each gamete contain one allele from a parent
This makes 4 possible outcomes from 2 parents.
Speciation
Fossils provide evidence that animals and plants change over long periods of time.
Bone and shells do not decay as easily.
Dead organisms can be preserved in amber, peat logs , tar pits or in ice
Casts and impressions such as foot prints gets covered by layers of sediment which becomes rock.
Simplier organisms are found at the oldest rocks
This supports the theory of evolution
Extinction
When individuals are poorly adapted to the environment they are less likely to survive and reproduce so they don't pass on the genes. If a species are poorly adapted the will become extinct as they will not survive.
Factors that can cause extinction
New disease
New predator
New competitor
Change to climate
Catastrophic event.
Isolation is when 2 population of species become geographically separated over time they become more adapted to their different environment and makes characteristics different.