Biology GCSE (2)

Plant and Animal cells have similarities and differences 

1) Nucleus- contains genetic material that controls the activities of the cell

2) Cytoplasm- Gel like substance where most chemical reactions happen

3) Cell membrane- Holds the cell together and controls what goes in/out

4) Mitochondria - where most of the reactions for respiration take place

5) Ribosomes- Where proteins are made

Extra things plant cells have that animal cells don't:

1) Cell wall - made of cellulose which supports and strengthens the cell

2) Permanent vacuole - Contains cell sap 

3) Chloroplasts - Where photosynthesis occurs which makes food for the plant and contains green substance called chlorophyll 

Cells make up Tissues, Organs and systems

Cells have specialised structures so they can carry out their function

Similar Cells are grouped together to make a tissue

Different tissues work together as an organ

Groups of organs work together to make up an organ system (e.g. Digestive)

Groups of organs and organ systems make up a full organism (e.g. Human)

Plant example

Palisade cells... make up palisade tissue... makes up a leaf(organ)... makes a plant (organism)

Palisade Leaf cells are adapted for photosynthesis

They're packed with chloroplasts for photosnthesis (at the top of the cell-nearer light)

Tall shaped- large surface area exposed downside for absorbing CO2 

Thin shaped- can pack a lot of them at the top of the leaf 

Guard Cells are adapted to open and close pores

Kidney shaped - opens and clsoes the stomata in a leaf

When the plant has lots of water the guard cells fill with it and go plump and turgid which makes the stomata open so gases can be exchanged for photosynthesis

When short of water the guard cells lose water and become flacid which closes the stomata this stops water vapour escaping 

Thin outer wall and thick inner wall to make opening/closing action 

Sensitive to light and close at night to save water without losing out on photosynthesis 

Red Blood cells are adapted to carry oxygen

Concave shaped- big surface area for absorbing oxygen and helps to pass through capillaries easily

Packed with haemoglobin- pigment that absorbs oxygen 

No nucleus- More room for haemoglobin

Sperm and Egg cells are specialised for reproduction

An Egg cell's function is to carry female DNA and to nourish a developing embryo

It contains huge food reserves to feed an embryo

When a sperm fuses with an egg the membranes change its structure to stop more sperm getting in 

This makes the offspring end up witht he right amount of DNA

The function of sperm is to get male DNA to the female DNA 

It has a long tail and streamline head to help it swim to the egg

A lot of mitochondria to provide energy needed 

Carry enzymes in their head to digest through the egg cell membranes 

Diffusion is the passive movement of particles from an areas of HIGH CONCENTRATION ro and area of LOW CONCENTRATION 

diffusion happens in liquids and gases as the particles are free to move about 

the bigger the difference in concentration the faster the rate of diffusion 

Cell membranes are clever

They hold together the cell but also let things in and out 

Substances can move in and out my diffusion or osmosis 

Only small molecules can diffuse through cells e.g. glucose, amino acids, water 

Particles flow through the cell memnrane from where there is a high concentration to a low concentration 

They go in both directions (randomly) but if there are more particles on one side of the membrane there is an overall movement from that side 

rate of diffusion depends on:

Distance- Substances diffuse more quickly when they dont have to move far 

Concentration difference- Substances diffuse faster if there is a big difference in concentration 

Surface area - the more surface area there is available for molecules to move across the faster they can get from one side to the other 

Osmosis is the movement of water molecules across a partically permiable membrane from a region of HIGH WATER CONCENTRATION to a region of LOW WATER CONCENTRATION 

A partially permiable membrane has very small holes in it, so small that only tiny molecules can pass through e.g. water. 

The water molecules pass both ways during osmosis

This is because water molecules can move about randomly all the time

Because there are more water molecules on one side there is a stead net flow into the region with fewer water molecules e.g. into strong sugar solution

This means the sugar solution gets more dilute- water is trying to even up the concentration of each side of the membrane

Osmosis is a type of diffusion

water moves into and out of cells by osmosis 

Tissue fluid surrounds the cells in the body - water, oxygen, gluse

it is squeezed out of the blood capillaries to the supply cells 

the tissue fluid usually has different concentration to the fluid inside the cell 

water will either move into the cell or out of the cell by osmosis 

if a cell is short of water, the solution inside will become concentrated so the solution outside is more dilute and will move into the cell by osmosis

If a cell has lots of water the solution inside will be more dilute and water will be drawn out of the cell by osmosis 

EQUATION FOR PHOTOSYNTHESIS

                                                               SUNLIGHT 

CARBON DIOXIDE + WATER >>> GLUCOSE +OXYGEN 

           CHLOROPHYLL 

photosynthesis produces glucose using sunlight

Photosynthesis is the process that produces food in plants (glucose)

It happens in leaves of all green plants

It happens inside the chloroplasts which are found in leaf cells and other green parts of a plant

Chloroplasts contain chlorophyll which absorbs sunlight and uses it's energy to convert Carbon Dioxide and water into glucose - oxygen is produced also 

Four things are needed for photosynthesis to happen

1) LIGHT

Usually from the sun

2) CHLOROPHYLL

Green substance which is found in chloroplasts and makes the leaves look green

it absorbs the energy in sunlight and uses it to combine CO2 and water to make glucose

3) CARBON DIOXIDE

Enters the leaf from the air around

4) WATER 

comes from the soil up the roots and stem and into the leaf 

the limiting factors depends on the conditions

1) At night time when LIGHT is a limiting factor

2) in winter, when TEMPERATURE is a limiting factor

3) if it is warm enough and bright enough, then CO2 is a limiting factor 

Not enough light slows down the rate of reaction

light provides energy needed for photosynthesis

as light level is raised rate of photosynthesis increases up to a certain point 

Beyond that it wont make a difference because either temperature or CO2 levels will become a limiting factor 

graph (1) 

Too little carbon dioxide also slows it down 

CO2 is one of the raw materials needed for photosynthesis 

The amount of CO2 will only increase the rate of photosynthesis up to a point and after this flattens out showing that CO2 is no longer a limiting factor 

graph

The temperature has to be just right

Usually if the temperature is the limiting factor it's because it is too low and the enzymes needed for photosynthesis work slower and low temperatures 

If the plant gets too hot the enzymes will become damaged

This happens at around 45 degrees 

graph 

1) for respiration

• plants manufacture glucose in their leaves
• they use some of the glucose for respiration
• they release energy which enables to convert the rest of the glucose into various other useful substances which they can use to build new cells and grow 
• To produce some of these substances they need to gather a few minerals from the soi

2) Making fruits

• Glucose and fructose (another sugar) is turned into sucrose for storing in fruits 
• Fruits deliberately taste nice so that animals will eat them and spread the seeds all over the place

3) Making cell walls

• Glucose is converted into cellulose for making cell walls 

4) making proteins 

• glucose is combined with nitrates to make amino acids
• these amino acids are then made into proteins

5) Stored in seeds

• Glucose is turned into lipids (fats and oils) for storing in seeds
• Sunflower seeds e.g. contain a lot of oil - we get cooking oil and margarine from them 

6) Stored as starch

• Glucose is turned into starch and stored in roots, stems and leaves ready for use when photosynthesis isn't happening e.g. winter
• starch is insoluble which makes it better for storing as it doesn't bloat the storage cells by osmosis like glucose

you need to know about 2 minerals in particular 

1) Nitrates

• They are needed for making amino acids which are then used to make proteins

2) Magnesium 

• It is needed to make chlorophyll which is needed for photosynthesis

Lacking theses minerals can cause deficiency symptoms

1) lacking nitrates - The plant starts to show stunted growth because proteins are needed for new growth 

2) lacking magnesium - The leaves of the plant will go yellow because magnesium is needed to make chlorophyll which gives the leaves a green colour 

You need to be able to construct a pyramid of biomass 

there's less energy and biomass every time you move up a stage in a food chain and there are usually fewer organisms

each bar on the pyramid shows the mass of living material at that stage of the food chain 

you need to be able to construct a pyramid of biomass

the big bar along the bottom represents the producer (e.g. plant) 

the next bar represents the primary consumer (the animal that eats the plant)

the next bar represents the secondary consumer etc... 

All that energy just disappears somehow...

energy from the sun is the source od energy for nearly all life on Earth

plants use small percentage od the light energy from the sun to make food during photosynthesis

respiration supplies the power for all life processes including movement. Most of the energy eventually lost to the surroundings as heat 

Some material which makes up plants and animals is inedible, so it doesnt pass to the next stage of the food chain material and energy are also lost from the food chain in excretion 

Elements are cycled back to the start of the food chain by decay

living things are made of materials they take from the world around them

Plants take elements like carbon, oxygen, hydrogen and nitrogen from the soil or air they turn these elements into complex compounds that make up living organisms

these elements are returned into the environment in waste products e.g. when the organism dies the material then decays because they're broken down by microorganisms

microorganisms work best in warm, moist conditions

All the elements are then recycled and return to the soil ready to be used by new plants and put back into the food chain again 

There are 2 ways to improve the efficiency of food production 

1) reduce the number of stages in the food chain

• You can produce a lot more food by growing crops rather than by having grazing animals, because you are reducing the number of stages in the food chain 

2) Restrict the energy lost by farming animals

• animals e.g. pigs and chickens and intensively farmed, they're kept close together indoors in small pens so they can't move
• this saves them from losing energy on movement which makes the transfer of energy from the animal feed to the animal more efficient
• this makes things cheaper. 

Some people think that forcing animals to live in unnatural and uncomfortable conditions is cruel. There is a growing demand for organic meat 

the crowded conditions on factory farms create environment for the spread of diseases like avian flu and foot and mouth

To try and prevent diseases animals are given antibiotics. When the animals are eaten these can enter humans which allows microbes that infect humans to develop immunity to those antibiotics

The environment where the animals are kept needs to be carefully controlled. The animals need to be kept warm to reduce the energy they lose in heat. This means using power from fossil fuels

our fish stocks are getting low but a lot of fish goes on feeding animals that are intensively farmed 

The carbon cycle shows how carbon is recycled

• There's only one arrow going down from the atmosphere the whole thing is powered by photosynthesis, CO2 is removed from the atmosphere by green plants and used to make carbs, fats and proteins in the plants 
• Some of the CO2 returned to the atmosphere when plants respire  
• Some of the carbon becomes part of the compounds in animals when the plants are eaten
• Some CO2 is returned to the atmosphere when the animals respire 
• When plants and animals die other animals (detritus feeders) and microorganisms feed on their remains and then CO2 is returned again 
• Animals produce waste which is broken down by detritus feeders 
• Carbon is constantly being cycled from the air through food chains and in the air again 

Enzymes are catalysts produced by living things

There are thousands of different chemical reactions going on inside all living things all the time

The reactions need to be controlled to get the right amount of substances 

You can make a reaction happen quicker by raising the temperature

there is a limit as to how far you can raise the temperature before the cells get damaged 

Living things produce enzymes which act as a biological catalyst. They reduce the need for high temperatures and we only have enzymes to speed up the useful chemical reactions in the body 

A CATALYST IS A SUBSTANCE WHICH INCREASES THE SPEED OF A REACTION WITHOUT BEING CHANGED OR USED UP IN THE REACTION 

All enzymes are proteins and they are made up of chains and amino acids which are folded into unique shapes.  

Enzymes have special shaped so they can catalyse reactions 

Chemical reactions usually involves things either being split apart or joined 

Every enzyme has a unique shape and fits onto the substance involved in a reaction 

Enzymes are picky, they only catalyse one reaction

This is because for an enzyme to work the substance has to fit a special shape and if the substance doesn't match the enzyme then the reaction wont be catalysed 

They need the right temp and pH                                                          

Changing the temp changes the rate of an enzyme-catalysed reaction            

If it gets too hot, the bonds holding the enzyme together break which destroys the enzyme's shape therefore it is now de-natured                                      

 They usually work best at 37degrees                                                                

If the pH is too high/low it interferes with the bonds and it denatures the enzyme                                                                                                              

 All enzymes have an optimum pH which is often 7

Respiration involves many different reactions which are catalysed by enzymes 

Respiration releases the energy that a cell needs to do everything

Respiration is not breathing in and out

It is the process of releasing energy from the breakdown of glucose and happens in every cell in the body

It happens in plants too, all living things respire and release energy from their food

RESPIRATION IS THE PROCESS OF RELEASING ENERGY FROMG LUCOSE WHICH GOES ON IN EVERY CELL 

Aerobic respiration is the respiration using oxygen, it is the most efficient way to release energy from glucose

Most reactions in aerobic respiration happen in the mitochondria 

GLUCOSE + OXYGEN >>>>> CARBON DIOXIDE + WATER +energy 

Respiration releases energy for all kinds of things

1. To build up larger molecules from smaller ones (e.g. proteins from amino acids)

2. In animals, to allow the muscles to contract which allows them to move

3. In mammals and birds the energy is used to keep their body temperature steady (as they are warm blooded)

4. In plants, to build sugars, nitrates, and other nutrients into amino acids, which are then built up into proteins 

AMYLASE converts STARCH into SIMPLE SUGARS in 3 places

1. The sailvary gland                                                                                          

2. The pancreas    

3. The smal intestine 

PROTEASE converts PROTEINS into AMINO ACIDS in 3 places

1. The stomach (pepsin)                                                                                        

2. The pancreas                                                                                                    

3. The small intestine 

LIPASE converts FATS into GLYCEROL and FATTY ACIDS in 2 places:

1. The pancreas                                                                                                    

2. The small intestine 

Digestive enzymes break down big molecules into smaller ones      

starch, proteins and fats and BIG molecules, They're too big to pass through the walls of the digestive system      

Sugars, amino acids, glycerol and fatty acids are much SMALLER molecules, They can pass through the walls of the digestive system

Bile neutralises the stomach and emulsifies fats

Bile is produced in the liver and is stored in the gall bladder before being released into the small intestine 

The hydrochloric acid in the stomach makes the pH too acidic for enzymes in the small intestines to work

Bile in alkaline so neutralises the acid and makes the conditions alkaline where the enzymes work best

It emulsifies fats- breaks it down into tiny droplets which gives it a bigger surface area which makes the digestion faster 

Salivary Glands - produce Amylase enzyme in the salvia 

Liver - Where bile is produced which neutralises stomach acid and emulsifies fats 

Gall bladder - Where bile is stored before being released in the small intestines 

Large Intestine - Where excess water is absorbed from the food

Rectum - Where the faeces are stored before going to the anus 

Stomach - It pummels the food with it's muscular walls, It produces the protease enzyme (pepsin), It produces hydrochloric acid to kill bacteria and to give the right pH for the protease enzyme to work 

Pancreas - Produces protease, amylase and Lipase enzymes and releases them into the small intestine 

Small intestine - Produces protease, amylase and lipase enzymes to complete digestion and this is where food is absorbed out of the digestive system into the body 

They are used in biological detergents

They are mainly protein-digesting enzymes (proteases) and fat digesting enzymes (lipases) 

Because they attack animal and plant matter, they're ideal for removing stains like food or blood

Enzymes are used to change foods 

The proteins in some baby foods are pre-digested using proteases so they're easy for the baby to digest

Carb-digesting enzymes (carbohydrases) can be used to turn starch syrup into sugar syrup

Glucose syrup can be changed into fructose syrup using an isomerase enzyme and as fructose is sweeter you use less of it 

using enzymes in industry takes a lot of control

They speed up reactions without the need for high temperatures and pressures

advantages of using enzymes:

They're specific and only catalyse the reaction that you want them to          

Using a lower temp/pressure means a lower cost and saving energy

They are biodegradable and therefore cause less environmental pollution 

Disadvantages of using enzymez

Some people can develop allergies to the enzymes

They can be denatured by a small increase in temp 

They are susceptible to poisons and change in pH so conditions have to be tightly controlled 

Contamination of the enzyme can affect the reaction 

HOMEOSTASIS IS THE MAINTENANCE OF A CONSTANT INTERNAL ENVIRONMENT 

There are 6 things that need to be controlled

1. The body temperature cant get too hot/cold

2. Water content mustn't get too high/low - too much water could move in/out of cells and damage them

3. If the ion content of the body is wrong the same could happen 

4. The blood sugar level needs to stay within certain limits 

5. Carbon dioxide  is a product of respiration and has to be removed and leaves the body by the lungs when you breathe out

6. Urea is a waste product from excess amino acids 

Body temp must be carefully controlled 

Enzymes in the human body work best at around 37 degrees and if the body gets too hot/ cold the enzymes will not work properly

1. There is a thermoregulatory centre in the brain which acts as your own personal thermostat 

2. it contains receptors that are sensitive to temp of the blood flowing through the brain 

3. The thermoregulatory centre also receives impulses from the skin, giving info about the skin's temp 

4. If you're getting too hot/cold your body can respond to cool you down/warm you up

When you're too hot:

1. Hairs lie flat

2. Sweat is produced by the sweat glands and evaporates from the skin which removes heat

3. The blood vessels supplying the skin dilate so more blood flows close to the skin which makes it easier for heat to be transferred from the blood to the environment 

When you're too cold:

1. Hairs stand up to trap an insulating layer of air 

2. No sweat is produced

3. Blood vessels supplying skin capillaries constrict to close off the skin's blood supply

4. you shiver which needs respiration which releases some heat energy 

The kidneys perform 3 main roles:

1. Removal of urea from the blood

2. Adjustment of ions in the blood

3. Adjustment of water content of the blood

1. Removal of urea:

Proteins can't be stored by the body so excess amino acids are converted into fats and carbs which can be stored. 

This process occurs in the liver. Urea is produced as a waste product from the reactions

Urea is poisonous, it's released into the bloodstream by the liver. The kidneys then filter it out of the blood and it's excrete from the body in urine 

2. Adjustment of Ion content

Ions e.g. sodium are taken into the body in food and then absorbed in the blood

If the ion content is wrong it could mean too much/ little water is drawn into the cells by osmosis. Which could damage the cells

Excess ions are removed by the kidneys e.g. a salty meal will contain too much sodium, so the kidneys remove excess sodium ions from the blood

Some ions are lost in sweat ( which tastes salty )

The balance is always maintained by the kidneys 

3. Adjustment of Water Content 

Water is taken into the body as food/drink and is lost in 3 main ways

1. Urine

2. Sweat

3. The air we breathe out 

Our body has to constantly balance the water coming in against water going out. Our bodies can't control how much we lose when we breathe but we control other factors. Water balance is between:

1. Liquids consumed

2. Amount sweated out

3. amount excreted by the kidneys in the urine

Insulin controls blood sugar levels

1. Eating foods containing carbs puts glucose into the blood from the gut

2. Normal metabolism of cells removes glucose from the blood

3. Vigorous exercise also removes a lot of glucose from the blood

4. Levels of glucose in the blood must be kept steady. Changes in the blood glucose level is controlled by the pancreas using the hormone insulin:

BLOOD GLUCOSE LEVEL TOO HIGH= INSULIN IS ADDED

BLOOD GLUCOSE LEVEL TOO LOW = INSULIN IS NOT ADDED 

Diabetes (type 1) - the pancreas stops making enough insulin

1. Diabetes is a disorder where the pancreas doesn't produce enough insulin

2. The result is that a person's blood sugar can rise to a level that can kill them 

3. It can be controlled in 2 ways

1. Avoiding foods rich in simple carbs, and to take exercise after eating carbs    so you use up the extra glucose. 

2. Injecting insulin into the blood at meal times. Which makes the liver remove     the glucose as soon as it enters to blood when the food is being deigested .           This stops the level of glucose from getting too high

4.  the mount of insulin that needs to be injected depends on the person's diet

5. Diabetics can check their blood sugar using a glucose-monitering device where they have to ***** their finger to get a drop of blood for the machine to check. 

Chromosomes are really long molecules of DNA 

1. DNA stands for deoxyribose Nucleic Acid

2. it contains the instructions to put an organism together and make it work

3. It's found in the nucleus of animal/plant cells in long molecules called chromosomes

A gene codes for a specific protein

1. A gene is a section of DNA and contains instructions to make a protein

2. Cells make proteins by stringing amino acids together in an order  

3. Only 20 amino acids are used and they make up thousands of proteins

4. Genes tell cells in what order to put the amino acids together 

5. DNA determines what proteins the cell produces e.g. haemoglobin 

6. That determines what type of cell it is e.g. red blood cell. 

Everyone has unique DNA

DNA Fingerprinting is a way of cutting up a person's DNA unto small sections and then separating them.

Everyone has a unique pattern. This means you can tell people apart by comparing samples of their DNA

DNA Fingerprinting is used in:

1. Forensic science - DNA taken from crime scenes is compared with DNA taken from a suspect 

2. Paternity testing - To see id a man is the father of a child

Mitosis makes new cells for growth and repair and asexual reproduction uses mitosis 

Humans have 23 pairs of chromosomes 

When a body cell divides it makes new cells identical to the original with the same number of chromosomes 

This type of cell division is mitosis and is used when plants/animals grow/replace damaged cells. 

1. The cell duplicates and forms X shaped chromosomes and each arm is a duplicate of the other

2. The chromosomes line up at the centre and cell fibres pull them apart, the 2 arms of each chromosome go to opposite ends of the cell

3. Membranes form around each of the sets of chromosomes and become the nuclei of the new cells

4. The cytoplasm divided and you have 2 new cells that are identical 

Gametes have half the number of chromosomes

In sexual reproduction gametes have 1 copy of each chromosome so they can be combined

Meiosis involves 2 divisions 

1. The cell duplicates - exact copies of each arm

2. 1st division - Pairs line up in the centre of the cell 

3. the pairs are pulled apart so each cell has one copy of each chromosome

4. Each new cell has a mix of the mums/dad's chromosomes (creates variation) 

5. In the second division the chromosomes line up again in the centre and the arms are pulled apart again

You then get 4 gametes with a single set of chromosomes in it 

Embryonic stem cells can turn in to any type of cell 

1. Most cells in the body are specialised

2. Differentiation is the process by which a cell changes to become specialised for it's job. In animals, they lose the ability to differentiate early but some plants never lose the ability

3. Some cells un-differentiate so they can develop into different types of cell - these are called STEM CELLS

4. Stem cells are found in human embryos and have the potential to turn into any type of cell 

5. Adults have stem cells but they are only found in certain places

• bone marrow 

Stem cells may be able to cure diseases 

The cells can be used to replace faulty cells in sick people e.g. nerve cells for someone that is paralysed

Some people are against stem cell research

1. Some people feel embryos shouldn't be used for experiments as it is potential human life

2. Embryos used are usually unwanted ones from fertility clinics, therefore if they weren't used for research would be destroyed

3. Campaigners feel that scientists should concentrate on developing other sources of stem cells 

4. In some countries it is banned but is allowed in the UK 

Your chromosomes control whether you're male or female

ALL MEN HAVE AN X AND Y CHROMOSOME: XY

THE Y CHROMOSOME CAUSES MALE CHARACTERISTICS 

ALL WOMAN HAVE 2 X CHROMOSOMES: **

THE ** COMBINATION ALLOWS FEMALE CHARACTERISTICS TO DEVELOP

The X and Y chromosomes are drawn apart in the first division in meiosis. 

There is a 50% chance each sperm has an X chromosome and 50% chance each sperm has a Y Chromosome

Mendel did Genetic Experiments with Pea Plants 

He noticed how characteristics in plants were passed on from one generation to the next 

Mendel had shown that the height characteristics in pea plants were determined by separately inherited "Hereditary Units" Passed on from each parent. The ratios of tall and dwarf plants in the offspring showed that the unit for tall plants T was dominant over the unit for dwarf plants, t 

Mendel reached 3 important conclusions

1. Characteristics in plants are determined by "Hereditary Units" 

2. Hereditary Units are passed on from both parents, one unit from each parent 

3. Hereditary Units can be dominant or recessive - if an individual has both the dominant and the recessive unit for a characteristic, the dominant characteristic will be expressed 

Hereditary units are - GENES 

Cystic Fibrosis is caused by a recessive Allele

It is a genetic disorder of the cell membranes and results in the body producing a lot of sticky mucus in the air passages in the pancreas 

1. The allele that causes it is recessive 'f' carried by about 1 in every 30 people 

2. Because it is recessive, people with only one copy of the allele wont have the disorder, they will be a 'carrier' 

3. For a child to have the disorder, both parents must be either carriers or sufferers

4. there is a 1 in 4 chance in having the disorder if both parents are carriers 

Huntingdon's is caused by a Dominant Allele 

It is a genetic disorder of the nervous system that results in shaking, erratic body movements and mental deterioration 

1. It is caused by a 'dominant' allele 'N' and so can be inherited if just one parent has the defective gene. 

2. The 'carrier' parent will be a sufferer as the allele is dominant, but the symptoms don't start until after the person is around 40

3. The person carrying the N allele has a 50% chance of passing it on to each of their children.  

Embryos can be screened for genetic disorders

for:

1. It will help to stop people suffering

2. There are laws to stop it going too far 

3. During IVF most embryos are destroyed so screening just allows one to be healthy

4. Treating disorders cost the government and tax payers a lot of money 

against

1. There may come to a point where everyone wants to screen their embryos so they can pick the most desirable one 

2. The rejected embryos are destroyed 

3. It implies that people with genetic problems are undesirable (prejudice)