Biology B2

Chromosomes- have long strands of DNA stored in the nucleus, these carry genes.

Genes- sections of DNA that code for specific characteristics, that are inherited from parents.

DNA- double helix structure made up of different base pairs carrying instructions to make proteins.Base pairs- grouped into 3- one group of 3 codes for 1amino acid. Proteins are made up of these amino acids

Base pairs- grouped into 3; one group of 3 codes for 1 amino acid. Proteins are made up of these amino acids.

Alleles are different variations of the same gene.

If the two alleles for a gene are the same, the gene is homozygous- either homozygous dominant or recessive.

If the two alleles are different, the gene is heterozygous.

If the gene is heterozygous, the capitalised (dominant) characteristic will be displayed in the phenotype.

• Biologica detergents (protien digesting enzymes [protease], Fat digesting enzymes [Lipase])
• Ideal for removing stains such as blood
• Effective at low temperatures
• However, some have allergies to these.
• Carbohydrase used to turn starch syrup into sugar syrup.
• Isomerase used to turn glucose into fructose in 'slimming foods'

Aerobic respiration- needs plenty of oxygen to take place but-

Glucose + Oxygen ~ Carbon dioxide + Water + ENERGY

Exercising increases the heart rate. Glycogen is used during the exercise as energy.

Anaerobic respiration- respiration without oxygen:

Glucose ~ ENERGY + Lactic Acid.

Lactic acid builds up in the muscles due to the incomplete breakdown of glucose, causing muscle fatigue. 

Anaerobic respiration leads to oxygen debt. Oxygen debt is normalised by blood flowing around the body and oxidising the lactic acid. While high levels of Co2 and lactic acid remain detected in the blood, pulse and breathing rate remain high. 

Bile is produced by the liver and stored in the gallbladder.

It is then released into the small intestine.

Bile is an alkaline and it neutralises the acidic conditions in the stomach, making the conditions suitable for the enzymes to work.

Bile emulsifies fats, breaking them into small droplets, meaning they have a larger surface area for lipase to work on, so the rate of digestion increases. 

In the digestive system:

• Salivary glands produce amylase
• Gall bladder stores bile
• Stomach produces pepsin-protease, also produces HCL to kill off bacteria, correct the pH for protease to work
• Pancreas produces amylase, protease and lipase
• Small intestine produces protease, lipase, amylase and absorbs food into the blood.

Mitosis is a form of asexual reproduction in cells, creating new cells for growth and repair. Two identical offspring are produced, with no genetic variation in the offspring.

Process:

1. DNA spread out in the cell in long strings in chromosones.

2. If the cell is signalled to divide, the DNA duplicates and forms x shaped chromosones.

3. Chromosones line up in the center of the cell and cell fibres pull each half of each x shape apart.

4. Membranes form around each set of chromosones, which becomes the nuclei of the new cell.

5. Cytoplasm divides and 2 new cells are fully formed. 

Meiosis is a variation of cell division that occurs within gametes, producing four cells with half the number of chromosomes. Process:

1. As with Mitosis, before the cell starts to divide it duplicates it's DNA.

2. In the first division, the chromosome pairs line up in the centre of the cell.

3. The pairs are then pulled apart by cell spindle fibres, with each of the new cells having the usual number of chromosomes for a non-gamete cell.

4. The cell then lines up again and the division repeats without duplicating. 

5. Four cells with half the regular number of chromosomes are produced. 

Cystic fibrosis is caused by a recessive allele, carried by 1 person in 25. People carrying only 1 copy of the allele will not be affected by the disorder but may pass it on. Thes are called carriers.

There's a 1 in 4 chance of the child having the disorder if both the parents are carriers:

This is a punnet square to show the probability of a offspring having cystic fibrosis if both parents are carriers.

Each regular human body cell has 22 matched pairs of chromosomes, with the 23rd pair being either ** or XY.

Men have XY chromosomes, with the Y chromosome causing male characteristics to be displayed.

Women have ** chromosomes, allowing female characteristics to develop. 

In sperm development, the X and Y chromosomes are pulled apart in the first division of meiosis. There's a 50% chance each sperm gets an X chromosome and a 50% chance each sperm gets a Y chromosome to match with the egg cell's single X chromosome.

In egg cell development the same process happens except with the original chromosome holding two ** chromosomes instead of an XY so there's no possibility of a single Y chromosome being present in the cell until fertilisation.

Hence the probabilities for the biological gender of a baby is 50% to each gender. 

Stem cells are cells that have the potential to differentiate into any other type of cell, incuding specialised ones. Stem cells can be found in adults in the bone marrow and is usually extracted from the hip. Embryos have many pluripotent stem cells in their early stages of development.
Ethical issues with embryonic stem cell research

• Some see the embryo as having the same rights as a human being
• Some see the termination of the embryos after research as taking a life
• Some are concerned over the fact that embryos can't consent to the research and being used for this purpose.

Until recently, the only way to get pluripotent stem cells was from embryos, but they can now be made from stimulating adult stem cells.

Differences between plant and animal cells:

Animal cell contains:

• Nucleus (controls cell fuction)
• Cytoplasm (contains enzymes, chemical reactions happen here)
• Cell membrane (holds cell together, controls intake and outake)
• Mitrochondria (release energy, site of respiration)
• Ribosomes (site of protien synthesis)

Plant Cells have all the above AND:

• Cell wall (suppoorts cell, made of culluose)
  
• Vacuole (contains cell sap, kepps cell rigid)
• Chloroplasts (Photosynethesis occurs here, contains chlorophyll)

Exceptions- Yeast has no mitrochondria and a bacterisl cell has no nucleus, but does have flagella. 

These enzymes break down large molecules of starch, proteins and fats into smaller molecules that are able to pass through the walls of the digestive system. 

Amylase converts starch into sugars

Protease converts proteins into amino acids

Lipase converts lipids into glycerol and fatty acids.

Amylase is found in:

• Salivary glands, Pancreas and rhe small intestine

Protease found in:

• Stomach (as pepsin), pancreas and small intestine

Lipase found in:

• Pancreas and small intestine

Similar cells are organised into tissues

• Muscular tissue- contracts to make what it's attached to
• Glandular tissue- makes and secretes chemicals eg enzymes and hormones
• Epithelial tissue- covers some parts of the body eg stomach lining

Uses in the stomach:

• Muscular tissue helps digest food
• Glandular tissue produces digestive juices
• Epithelial tissue covers the inside and outside of the stomach.

An organ system is a group of organs working together to perform a particular function. 

The Red Blood Cell (RBC)

• Concave shape allows for maximum surface area for oxygen absorption
  
• Contains haemoglobin, a protein that helps bind oxygen
• Has no nucleus- maximum surface area for oxygen absorption

Gametes: Egg cell:

• High levels of 'food reserves' to help embryo
• Membrane changes to block sperm after fertilisation

Sperm Cell:

•  High levels of mitochondrial reserves near the tail
• Long tail and stretched head 
• Enzymes in head to digest egg membrane

Cells become specialised through differentation. 

Diffusion is the spreading of gas and liquid particles from areas of high concentration to areas of low concentration, down the concentration gradient. 

Dissolved substances can move in and out of the cell by diffusion. 

Big molecules like proteins and starch won't fit through the cell membrane, but small molecules like amino acids and oxygen can. 

Palisade leaf cells have:

• High chloroplast content for photosynthesis
• High surface area
• Thin shape for high palisade vontent on top of leaf.

Guard cells: 

•  Shape allows opening and closing of the stomata, sensitive to light and will close at night. 
•  Allows gasses to be exhanged for photosynthesis and can lose water and become flacid

Plants contain:

Mesophyll tissue- where photosynthesis occurs 

Xylem and phloem- transport water and nutrients 

Epidermal tissue- covers the plant 

Photosynthesis:  NEEDS SUNLIGHT

Carbon dioxide + water ~ Glucose + oxygen

3 Limiting factors: 

Light

Volume of carbon dioxide

Temperature

When Light and carbon dioxide are the limiting factors for photosynthesis, they will increase the rate up to a point, then they will no longer be the limiting factor for photosynthesis.

When the temperature is the limiting factor, it will increase the rate of photosynthesis up to a point when the temperature is high enough to make the enzymes denature, so the rate of photosynthesis slows to stop. 

• Quadrats can be used for small organisms and for comparing the known number of organisms in an area with another one.

• Transects are used to study distribution along a line, mainly done with measurements at a constant interval.

Enzymes are catalysts produced by living things- biological catalysts. 

They increase the speed of reactions without being used up. They're also specific to the reaction they're catalysing. 

• Enzymes are proteinsmade up of amino acids
• They have an active site with the substrate fits into during the reaction.
• The enzyme then breaks down the substrate and it is then released, and the enzyme isn't used up.

Temperature and pH both affect enzymes. They denature at temperatures above 37 degrees celsius. 

Plants use Glucose for:

Respiration- enabaling plants to convert the rest of the glucose to useful substances using the energy from respiration, enabling the plant to grow.

Glucose is converted to cellulose to make string cell walls

Glucose and nitrate ions make amino acids and proteins

Glucose is converted into lipids for storing in seeds. 

Glucose is turned into starch and stored in the plant roots. 

Greenhouses:

• Trap the sun's heat with glass windows
• Have a heater in winter, ventilation in the summer to control heat
• Artificial light to maximise photosynthesis
• Paraffin heater increases carbon dioxide levels
• Fertilisers used in soil.

Natural selection- organisms better adapted to their environment tend to survive and pass on successful genes, producing more offspring. This is theorised to be the main process that will bring about the evolution of a species. 

Evolution- development and adaptation of a species to their environment. 

Species- a group of animals that can produce fertile offspring with each other. 

Speciation comes about through isolation and adaptation of different populations to their environment:

• A population becomes isolated by a geographical barrier/habitat loss/human interference
• Each population adapts to their new habitat- evolution takes place by natural selection favouring the adaptations (genes) that best help survive in the individual's habitat.
• The two populations then develop over time to adapt to their environment and can no longer successfully interbreed, so two new species has been formed.

Fossils are the remains of plants and animals, found in rocks and formed over millions of years. Fossils are formed by:

• Gradual replacement of minerals- teeth, shells, bones are gradually replaced by minerals in rocks and form a rock-like substance, staying distinct in the rock
• Casts and impressions- clay hardens around the organism as it decays, leaving a cast of its self.
• Preservation in places of no decay- tar pits there's no oxygen for decay to take place, in glaciers it's too cold for the decay process to start and peat bogs are too acidic to decay microbes.

Fossils don't often show transition species.