Biology Paper 1 I think celll biology

Describe eukaryotic cells (plant and animal cells)

Cells that contain a nucleus that encloses DNA(genetic information) and other organelles

What are eukaryotes?

Organisms that are made up of eukaryotic cells e.g. plants or animals.

What is a prokaryote?

A single-celled organism which doesn’t store genetic information in a nucleus e.g. bacteria + Significantly smaller than a eukaryotic cell

What do Prokaryotic cells contain?

Single Loop of DNA

Plasmids=Small rings of DNA

Cytoplasm

What is a Bacterial Cell(prokaryotic)?

Don’t have a nucleus & their genetic material is a single Loop of DNA.

MAY ALSO HAVE:

Small rings of DNA = Plasmids

Size of Cells

Centimetres (cm):

1 Metre (m) / 100 = 1 cm

Millimetres (mm):

1 cm / 10 = 1mm

Micrometers (μm):

1 M /1,000,000 = 1 μm

Commonly used to measure: size of cells & their components

Nanometers (nm):

1 M / 1,000,000,000 = 1 nm

Used to measure : size of smaller cellular components (e.g protein)

What does an animal cell consist of?

• Nucleus

• Mitochondria

• Cell membrane

• Cytoplasm

• Ribosomes

What does a plant cell consist of?

• Nucleus

• Mitochondria

• Cell membrane

• Cytoplasm

• Ribosomes

• Rigid cell wall

• Chloroplasts

• Permanent vacuole

What does a bacterial cell consist of?

• cell membrane

• cell wall

• cytoplasm

• circular strand of DNA

• plasmids

Function of nucleus

Contains genetic material that controls the activities of the cell

Function of mitochondria

These are where most of the reactions for aerobic respiration take place.

Respiration transfers energy that the cells need to work.

Function of cytoplasm

Gel-like substance where most of the chemical reaction happen.

It contains enzymes that control these chemical reactions.

Function of cell membrane

Holds the cell together and controls what enters and leaves the cells

Function of ribosomes

Site of protein synthesis

- These are where proteins are made in cells

Describe the cell wall in plants and it’s function

• Made of cellulose

• Gives the plant cell it’s shape and strengthens it.

Describe the permanent vacuole and it’s function

• Contains cell sap ( a weak solution of sugars and salts) which helps keep cell turgid

Describe the chloroplasts and their function

• Contain chlorophyll which is the site of photosynthesis

• Also contains enzymes needed for photosynthesis

• Also provides colour green

Animal cell specialisation

• Most animals cells are specialised.

• This means that they have adaptations which help them to carry out their particular function.

• When cells become specialised, scientists call that differentiation.

How are sperm cells specialised to carry out their function?

Function: To join with an ovum (egg cell) in a process called fertilisation. During fertilisation the genetic information of the ovum and the sperm cell combine.

Adaptations:

1. Contain only half the genetic information of a normal adult cell.

2. Sperm cells have a long tail = allows them to swim to the ovum.

3. Streamlined head = swim to the ovum.

4. Sperm cells are packed full of mitochondria = transfer the energy needed for the tail to move

5. The outer layer of the sperm head (acrosome) stores digestive enzymes= can break down the outer layer of the ovum.

How are nerve cells specialised to carry out their function?

Function: To send electrical impulses around the body.

Adaptations:

1. Long axon= carries electrical impulses from one part of the body to another, to cover more distance

2. Axon is covered in myelin=insulates the axon and speeds up the transmission of nerve impulses.

3. Synapses=(The end of the axon)= junctions which allow the impulse to pass from one nerve cell to another.

4. Dendrites=increase the surface area so that other nerve cells can connect more easily.

How are muscle cells specialised to carry out their function?

Function: To contract (get shorter) quickly

Adaptations:

1. Contain protein fibres which can change their length

2. When muscle cell contract these protein fibres SHORTEN=decreasing the length of the cell

3. Have lots of mitochondria = transfer energy needed for contraction.

4. Work together to form =muscle tissue

5. They can store glycogen( a chemical that can be broken down into glucose and used in cellular respiration).

Plant cell specialisation

• Most plant cells are specialised.

• They have special adaptations which help them to carry out their particular function.

• When cells become specialised =that process is called differentiation.

Specialised root hair cell + Function:

Function: Absorbing water and minerals

Adaptations:

1. Have root hairs = increase surface area available so it can absorb water +dissolved minerals

2. Don’t contain chloroplast as underground

3. Have= large permanent vacuole that speeds up the movement of water by osmosis.

4. Have many mitochondria that transfer the energy needed for the active transport.

Xylem Cells Specilaised+ function:

Found in: Pants stem

Form:Long tubes

Function: To carry water and dissolved minerals ions from the roots to the leaves.

Adaptations:

1. The end walls in xylem cells are broken down forming a long tube so water and dissolved minerals can easily flow through.

2. Xylem cells have no nucleus ,cytoplasm or vacuole, no organelles ALLOWs=water & dissolved minerals to flow through more easily.

3. Thick walls which Contains lignin: makes xylem cells very strong & help support plant (but as cell walls are covered in lignin) =causes xylem cells to die

Xylem Specialisation + its function

Functions: To carry dissolved sugars up+down plant & from the leaves to other parts of the plant (consist of 2 diff types of cells)

Adaptations:

1. (Cell 1)Phloem vessel cells =very few sub cellular structures to help the flow of substances.

2. Phloem vessel cells have NO nucleus +only limited cytoplasm

3. (Cell 2)Sieve plates = (broken cell walls=sieve plates)=Allows dissolved sugars to move through cell interior

4. Phloem vessel cell has a companion cell connected by pores=provide energy to transport substances in the phloem.(mitochondria in comp. Cel provides energy to phloem vessel cell)

How to use a Optical Microscope to view a prepared slide

1)Place slide onto stage , use the clips to hold the slide in place

2)Then select the lowest power objetive lens (usually 4*)

3) Using the ‘coarse focussing dial’ slowly turn to position objective lens almost touching the microscope slide

4)Look through eyepiece and slowly turn the ‘coarse focussing dial’ which increases the distance between the ‘objective lens’ and the ‘slide’ until cells come into focus

5)Use ‘fine focusing dial’ to bring cells into a clear focus

6) work out total magnification =‘Eye piece lens’*’objective lens’

7)Adjust ‘fine focussing dial’ to bring cells back to focus

8)Use a pencil to make a clear, labelled drawing of some of the cells & include magnification scale

9)Mag. Scale = place a clear ruler over the stage =measure the diameter it in ‘millimetres’ and include the magnification

OPTICAL MICROSCOPE CAN ONLY SHOW LIMITED DETAIL :no ribosomes etc

Calculate the Total Magnification

Multiply the magnification of the eyepiece lens * magnification of the objective lens

‘Eye piece lens’ magnification= 10x

‘Low-power objective lens’ magnification=4x. 10×4 = total mag.=40x

REQUIRED PRACTICAL 1:

MICROSCOPE

1)Using forceps

Disadvantages of light microscopes

• They have limited magnification

• Limited resolution (image is blurred)

How to use an optical microscope to view a prepared slide

Resolution

• The shortest distance between two points on an object, that can still be distinguished as two separate entities.

• A measure of how detailed the image is.

Advantages of electron microscope

• Greater magnification (than light microscopes)

• Greater resolution (than light microscopes)

Equation for magnification

magnification= size of image/ size of real object

Where do we find chromosomes?

In the nucleus

What does an agar gel plate contain?

• Nutrient broth- which contains all the nutrients that the bacteria need to grow and divide.

• The nutrient broth has been set into a jelly using a chemical called agar.

• This is then poured into a petri dish and allowed to set.

What are chromosomes made out of?

The molecule DNA?

How many of each chromosome do body cells contain?

Two-they’re paired

• except gametes

How many pairs of chromosomes do human body cells contain?

23

Which certain cell has chromosomes which are not paired?

Gametes- They have 23 single chromosomes

What do chromosomes carry?

Genes- which determine many of our features

Cell division by mitosis

1. The DNA replicates to form two copies of each chromosome. The cell also grows and copies it’s internal structure, such as mitochondria and ribosomes.

2. Then (mitosis takes place.) One set of chromosomes is pulled to each end of the cell. The nucleus also divides.

3. The cytoplasm and cell membrane divide to form two identical daughter cells.

What is the cell cycle?

When a cell divides in a series of stages.

Functions of mitosis

• Mitosis is essential for growth and development of multicellular organisms (e.g. plant and animals).

• Mitosis takes place when an organism repairs itself (e.g. when a broken bone heals).

• Mitosis happens during asexual reproduction.

What is a stem cell?

A undifferentiated cell of an organism which has the potential to develop+differentiate to form certain other types of cells.

What are embryonic stem cells?

Stem cells in early human embryos.

They’re capable of turning into any type of body cell.

Used to treat conditions w/o rejection of human body

Where can adult stem cells be found?

Bone marrow

Why is bone marrow different to embryonic stem cells?

Adult stem cells cannot differentiate into any type of cell-only certain types: such as cells found in blood: red blood cells, white blood cells and platelets.

What is leukaemia?

A cancer of the bone marrow.

How does medicine use bone marrow?

Stem cells transferred from the bone marrow of a healthy person can replace faulty blood cells in the patient who receives them.

1) patients existing bone marrow is destroyed using :RADIATION

2)Patient receives a transplant of bone marrow from donor

3)Stem cels in bone marrow DIVIDE & FORM NEW bone marrow —also DIFFERENTIATE & form BLOOD cells

Problems with bone marrow transplant

• Donor must be compatible with the patient — otherwise white blood cells produced by the donated bone marrow could attack the patient’s body.

• Viruses can be passed from the donor to patient.

• Procedure can be painful

Two ways stem cells can be used in medicine

• Bone marrow transplant

• Therapeutic cloning (embryo )

What is produced in therapeutic cloning?

An embryo with the same genes as the patient.

Therapeutic cloning

1)embryo is produced with the same genes as the patient.

2)Stem cells from the embryo can be transplanted into patient without being rejected by the patient’s immune system.

Once inside the patient, the stem cells can then differentiate to replace cells which have stopped working correctly.

What can therapeutic cloning be used for?

A whole range of medical conditions such as diabetes or paralysis

• diabetes- check key cards

Disadvantages of therapeutic cloning

Some people have ethical objections to this procedure as embryos are destroyed in process and people view embryos as potential life.

What can meristem tissue in plants do?

Differentiate into any type of plant tissue, at any point in the life of the plant.

What can meristem tissue be used for?

Stem cells from meristems in plants can be used to produce clones of plants quickly and economically.

• Rare species can be cloned to protect them from extinction.

• Stem cells can also be used to grow crops of identical plants that have desired features for farmers, e.g. disease resistance

What is diffusion?

Diffusion is the spreading out of particles resulting in a net movement from an area of high concentration to an area of low concentration.

Diffusion of O2 and CO2

Cells need oxygen for respiration, which is carried out by the mitochondria.

Cells are surrounded by a high concentration of oxygen as oxygen is transported into the bloodstream from the lungs.

The oxygen molecules move into the cell by diffusion from an area of high concentration to an area of low concentration.

The oxygen is used to generate energy in respiration and this produces the waste gas carbon dioxide.

That means there’s a higher concentration of carbon dioxide inside the cell than outside so the carbon dioxide moves out of the cell by diffusion.

What is urea?

A waste products produced inside cells.

Diffusion of urea

It diffuses out of the liver cells (high concentration) into the blood plasma (low concentration) and is excreted by the kidneys.

How does the concentration gradient affect the rate of diffusion?

The greater then concentration gradient, the higher the rate of diffusion.

How does temperature affect the rate of diffusion?

The higher the temperature, the greater the rate of diffusion, as the particles have more kinetic energy and are moving faster.

How does surface area affect the rate of diffusion?

The larger the surface area (of the cell membrane), the greater the rate of diffusion.

Surface area to volume ratio of amoeba

Amoeba are single-celled organisms. A single-celled organism has a relatively large surface area to volume ratio.

This allows sufficient transport of molecules into and out of the cell to meet the needs of the organism

As organisms get larger, what happens to the SA:V ratio

It decreases (this is a problem for multi-cellular organisms)

Problem of having a low SA:V ratio on multicellular organisms.

• Their surface area is not large enough for their volume.

• Cells on the surface can get enough oxygen simply by diffusion however, not enough oxygen can diffuse into the centre of the organisms as they’re too far away from the surface.

• Due to this, multicellular organisms have exchange surfaces and a transport system to solve this problem.

Describe how the gills in fish are adapted for exchanging materials.

Gills are covered in a very large number of fine filaments- where gases pass in and out of the blood. (Deoxygenated blood passes into the filament. Then oxygen from the water diffuses into the blood. Oxygenated blood is then returned to the body).

• Adaptations of filaments for efficient diffusion:

  • Give the gills a massive surface area

  • Thin membrane to provide a short diffusion pathway.

  • The filaments have an efficient blood supply to take the oxygenated blood away. This ensures that the concentration gradient is always high.

What is osmosis?

Osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.

What’s a partially permeable membrane?

A membrane than only allows some molecules to pass through.

Osmosis of animal cells

• The cytoplasm is a relatively concentrated solution so if an animals cell is placed into water, then osmosis will take place.

• In hypotonic conditions Water will move by osmosis from outside the cell to inside the cell.

• This causes the cell to expand or possibly burst.

• In hypertonic conditions If an animal cell is placed into a very concentrated solution, then water will move out of the cell by osmosis and the cell will shrink.

• In isotonic conditions there is no change

Osmosis of plant cell

• The cytoplasm is a relatively concentrated solution so if an plant cell is placed into water, then osmosis will take place.

• Water will move into the cell by osmosis and the cell will expand.

• Unlike an animal cell, plant cells have a cell wall which prevents the cell from bursting so the cell becomes turgid after water moves into it by osmosis.

• If a plant cell is placed into a concentrated solution, then water moves out of the plant cell by osmosis, causing the cell to shrink/become flaccid.

Describe how to use microscope to view a specimen

• Place slide onto stage and use the clips to hold the slide in place.

• Select the lowest power objective lens.

• Slowly turn the coarse focusing dial to focus the image, looking from the side not the eyepiece to prevent damage.

• Then look through the eyepiece and slowly turn the coarse focusing dial but this time increase the distance between the objective lens and the slide. Do this until the cells come into focus.

• Then use the fine focusing dial to bring the cells into clear focus.

• Change the objective lens to a higher power to observe image with higher magnification.

• Use a sharp pencil to make a sketch, and label all features and draw the features in proportion and include a scale bar.

How to calculate total magnification (with microscopes)?

Multiply the magnification of the eyepiece lens by the magnification of the objective lens.

How to prepare a slide for onion cells

1. Peel off epidermal layer using forceps

2. Place sample on drop of water on microscope slide

3. Add drops of iodine (methylene blue for cheek cells) solution to the sample.

4. Lower cover slip onto sample using mounting needles to ensure there aren’t air bubbles

What is active transport?

A process that moves substances from an area of low to high concentration (against the concentration gradient), using energy from respiration.

Effect of osmosis on plant tissue

1. Peel the potato, because the potato skin can affect osmosis.

2. Use a cork borer to produce three cylinders of potato. Using a cork borer makes all of the cylinders the same diameter.

3. Use a scalpel to trim the cylinders to the same length (around 3cm).

4. Measure the length and mass of each cylinder (using a ruler and balance)

5. Now add each cylinder unto a test tube. Add 10cm³ of 0.5 molar sugar solution into the first test tube.

6. Add 10cm³ of 0.25 molar sugar solution in the second test tube.

7. Add distilled water into the third test tube. (distilled water contains no dissolved substances which could affect the rate of osmosis)

8. Leave the potatoes overnight and allow osmosis to take place.

9. Next remove the potato cylinders and roll them on a paper towel to remove any surface moisture (which could affect mass. Also don’t press too hard so that you don’t force water out of cells).

10. Measure the lengths and the mass of the cylinders again and calculate the % change using the formula.

percentage change formula

% change- change in value/original value x 100

What does it mean when potato has no change in mass

Concentration of water inside and outside the cell was the same so no overall osmosis took place.

Tissue

A tissue is a group of cells with a similar structure and function.

Organ

An organ is a group of tissues working together for a specific function e.g. the stomach. The stomach contains muscle tissue and glandular tissue (which releases enzymes).

What are organs grouped into?

Organ systems which work together to form organisms.

Why are food molecules digested?

Because they are too large to be absorbed into the bloodstream.

What happens during digestion.

Large food molecules are broken down into small molecules by enzymes. These small molecules can then be absorbed into the bloodstream.

Now the products of digestion are then used by the body to build new carbohydrates lipids and proteins.

Some of the glucose produced is used in respiration.

The Digestive system

1. Food is chewed in the mouth. Enzymes in the saliva begin to digest the starch into smaller sugar molecules.

2. The food then passes down the oesophagus into the stomach. In the stomach, enzymes begin the digestion of proteins. The stomach also contains hydrochloric acid which helps the enzymes to digest proteins.

3. The food spends several hours in the stomach, The churning action of the stomach muscles turns the food into a fluid increasing surface area for enzymes to digest.

4. The fluid now passes into the small intestine and at this point chemicals are released into the small intestine from the liver and the pancreas. The pancreas releases enzymes which continue the digestion of starch and protein and they begin the digestion of lipids. The liver releases bile which helps to speed up the digestion of lipids as it emulsifies fats. Bile also neutralises the acid released from the stomach.

5. The fluid makes its way down the rest of the small intestine. The walls of the small intestine release enzymes to continue the digestion of proteins and lipids. In the small intestine, the small food molecules produced by digestion are absorbed into the bloodstream either by diffusion or active transport.

6. Now the fluid makes it’s way through the large intestine where water is absorbed into the bloodstream.

7. Finally the faeces is released from the body.

What are enzymes?

Large protein molecules.

They have a groove on their surface called the active site.

The active site is where the substrate attaches to.

The substrate is the molecule that the enzyme breaks down.

The lock and key theory

1. If the active site and substrate are complementary then the enzyme breaks down the substrate into the products.

2. Enzymes are specific- the substrate must fit perfectly into the active site.

3. Enzymes are not used up.

What do digestive enzymes do?

Digestive enzymes convert large food molecules into small soluble molecules that can be absorbed into the bloodstream.

What are proteins broken down by?

• Enzyme called proteases

• This is found in the: stomach, pancreatic fluid and small intestine.

What are proteins?

• Long chains of chemicals called amino acids.

• When we digest protein, the protease enzyme converts the proteins back to the individual amino acids, which are then absorbed into the bloodstream.

• When the amino acids are absorbed by the body cells, they are joined together in a different order to make human proteins.

What are carbohydrates broken down by?

Enzymes called carbohydrase- an example of this is amylase which breaks down starch.

Amylase is found in the saliva and pancreatic fluid and small intestine.

What is starch?

• A chain of glucose molecules.

• When carbohydrates like starch are digested, we produce simple sugars

What are lipids broken down by?

Enzyme called lipase

Lipase is found in the pancreatic fluid and the small intestine.

What is a lipid molecule?

• A molecule of glycerol attached to three molecules of fatty acids.

• When lipids are digested, we produce glycerol and fatty acids.

Bile

• Made in the liver but stored in the gallbladder.

• Used to speed up chemical reactions, but it’s not an enzyme.

• Bile emulsifies lipids- it converts large lipid droplets into smaller droplets. This massively increases the surface area of the lipid droplets which increases the rate of lipid breakdown by lipase.

• Bile is alkaline which allows it to neutralise stomach acid, creating alkaline conditions in the small intestine. This increases the rate of lipid digestion by lipase as the lipase work best in these conditions.

Effect of temperature on enzyme activity

• As temperature increases, enzyme activity increases/reaction gets faster.

• This is because the enzyme and substrate move faster at higher temperatures, so there are more frequent collisions between the substrate and the active site.

• At a certain temperature, the enzyme is working at the fastest possible rate- optimum temperature (usually 37 degrees for human enzymes, human body temperature).

• As we increase the temperature past the optimum, then the activity of the enzyme rapidly drops to 0 as the active site of the enzyme has been denatured.

• This is because, at high temperatures, the enzyme molecules vibrate and the shape of the active site changes, meaning that they no longer fit perfectly together and the enzyme can’t catalyse the reaction.

Effect of pH on enzyme activity

• The enzyme has an optimum pH where the activity is maximum.

• Each enzyme has a specific optimum pH

• If we make the pH more acidic or alkaline then the activity drops to 0.

• That’s because the active site denatures if the conditions are too acidic or too alkaline.

How is the small intestine adapted for absorbing the products of digestion?

• Very long (humans 5 metres) providing a very large surface area for absorption of the products of digestion. (increases diffusion rate)

• The interior of the small intestine is covered with millions of villi which massively increase the surface area for the absorption of molecules. (increases diffusion rate)

• On the surface of villi there are microvilli to further increase the surface area for absorption of molecules. (increases diffusion rate)

• Villi have a very good blood supply so the bloodstream rapidly removes the products of digestion, which increases the concentration gradient, increasing the rate of diffusion of molecules into the bloodstream.

• The villi have a very thin membrane which ensures short pathway for the diffusion of molecules.

• Any molecules that aren’t absorbed by diffusion are absorbed by active transport.

Circulatory system of fish

• Single circulatory system

• Blood is pumped from the heart to the gills where it collects oxygen and becomes oxygenated.

• Oxygenated blood passes straight from the gills to the organs where the oxygen diffuses out of the blood and into the body cells.

• The deoxygenated blood then returns to the heart.

What are the problems with a single circulatory system?

• The blood loses a lot of pressure as it passes through the different organs.

• This means that the blood travels to the organs slowly so it can’t deliver a great deal of oxygen.