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Access to HE (Health Studies) Cell Biology

Task 1

This table defines the seven characteristics of living thigs, including examples.

Characteristic Definition Examples

1) Movement

Each living organism has the ability to move and change position. An example of movement is a human using the muscles in its body to walk from one place to another

2) Respiration

Organisms that are living can create chemical reactions which can break down nutrient molecules to release energy.   An example of respiration is mitochondrion releasing energy as ATP in cells.

3) Sensitivity

Organisms can sense or detect stimuli and then respond to them accordingly. An example of sensitivity is a plant moving towards sun so the chloroplasts can absorbs the sunlight.

4) Nutrition

Every living organism can absorb nutrients, these nutrients can include mineral ions or organic substances. These nutrients contain energy or raw materials needed for tissue repair and growth.

An example of nutrition is a human eating a chicken breast and using the protein from the food to help growth, repair and maintenance in the body.

5) Excretion

All living organism can excrete excess substances, toxic materials and waste products of metabolism. An example of excretion is aerobic respiration.

6) Reproduction

Living organisms can reproduce to make more of the same organism. An example of reproduction is a sperm cell fertilising an ovum.

7) Growth

Every living organism can permanently increase their dry mass by increasing the number or size of cells within the organism.

An example of growth is a sunflower growing from just a seed.

Task 2

This diagram identifies the organelles in an animal cell:

This diagram identifies the organelles in a plant cell:

A) Vacuole

B) Cell wall

C) Rough endoplasmic reticulum

D) Nucleus

E) Mitochondrion

F) Chloroplast

G) Golgi apparatus

This diagram identifies the organelles in a bacterial cell:

A) Cell wall

B) Pili

C) Plasma membrane

D) Nuclear material

E) Flagellum

This table identifies and explains the structures and functions of cell organelles:

Organelle Structure Function

Mitochondrion Mitochondrion are bounded by two membranes that form an envelope around the matrix, this is where the enzymes involved in respiration are sited as well as DNA and ribosomes. They also have an inter-membrane space between the outer and inner membranes. The inner membranes have folds called cristae, these provide a large surface area for enzymes associated with ATP production needing oxygen. In plant cells mitochondrion are a similar size to the chloroplasts. The average size of mitochondrion is 2 micrometres. Mitochondrion act as mini power stations by releasing energy in a useable form (ATP) via aerobic respiration. This energy is then used to enable the cell to carry out all of its functions. Mitochondrion release energy in small amounts to avoid killing the cell. The more active a cell is the more mitochondrion it will have. Mitochondrion are passed down from the mother in animals.

Centriole Centrioles are an assembly of complex micro-tubes that occur in pairs. Centrioles form poles and spindles for cell division, these move the chromosomes apart during mitosis and meiosis.

Nucleolus The nucleolus is found inside the nucleus. Ribosomes are produced in the nucleolus.

Nucleus The nucleus is the largest organelle in an animal cell. The nucleus has a double membrane called the nuclear envelope that surrounds the nucleus. This nuclear membrane provides a selective barrier between substances in the nucleus and the cytoplasm. The nuclear pores allow the passage of large molecules to pass in and out of the cell.

Bacteria cells don’t have a nucleus because they have a lot less genetic material. The nucleus acts as the command centre of the cell by controlling all the cells functions. This organelle contains DNA in chromosomes which controls protein synthesis through mRNA.

Rough endoplasmic reticulum The endoplasmic reticulum consists of flattened membrane sacs, these are called cisternae. The surface of the RER is studded with ribosomes. The ribosomes in the RER produce proteins in the cisternae.

Plasma membrane The plasma membrane is made up of a lipid bilayer, proteins are embedded within this. The plasma membrane is a selectively permeable barrier that controls what comes into and out of the cell giving it the ability to constrict movement. Some substances pass through the membrane by diffusion, and others have their passage controlled by proteins. The plasma membrane is also a major site for the attachment of enzymes.

Ribosomes Ribosomes are the smallest organelle in plant cells, they are also smaller prokaryotic cells than in eukaryotic cells. This organelle is made up of a large and small sub-unit, which are both made up of protein and small complexes of RER. Carries out protein synthesis and transports the proteins through the membranes.

Golgi Complex/ Golgi Body/Golgi Apparatus This organelle is made up of a stack of flattened, membrane-bound sacs called cisternae. The cisternae are constantly being formed at one end of the organelle and are being pinched off as Golgi vesicles at the other end. Secretory cells have large Golgi bodies. The Golgi body produces glycoproteins, forms lysosomes, packages and secretes enzymes and forms cell wall material in plant cells.

Lysosome Lysosomes are made up of membrane-bound sacs. Lysosomes produce digestive enzymes which break down macromolecules and digests worn out cell components. Lysosomes have the ability to cause cell destruction if they’re ruptured.

Secretory vesicle Fuses with the plasma membrane. Releases materials to be secreted from the cell.

Vacuole The vacuole is a membrane-bound sack. Vacuoles are normally large in plant cells and small in animal cells.

Vacuoles store materials such as soluble pigments, excess water and waste products. They also provide support along with the cell wall when full – this only occurs in plant cells.

Cell wall The cell wall is made up of strong cellulose fibres in plant cells and murein in bacteria cells. Because the cell wall is rigid, plant cells are normally a regular geometric shape. The cell wall provides a rigid framework which gives essential support. The cell wall is not selectively permeable.  

Chloroplast Chloroplasts are only found in photosynthetic plant cells. They are flattened discs bounded by two membranes. Inside these membranes is membrane system made up of many flattened sacs called thylakoids. The thylakoids form stacks which are called grana. The grana contain chlorophyll, it is the chlorophyll that makes most plant cells look green.

The membrane system is surrounded by stroma, these are the site of enzymes that are used to make starch and sugars during photosynthesis. Chloroplasts are a similar size to the mitochondrion found in a plant cell. Chloroplasts are the site of photosynthesis. They absorb energy from sunlight and use it to produce food inside the cell. Chloroplasts have the ability to replicate independently.

Pili The pili or fimbriae are protein rods. These protein rods are concerned with cell-cell attachment.

Nuclear material The genetic material in a bacteria cell is composed of a circle of DNA. This genetic material is not enclosed within a nuclear membrane. This organelle contains the genetic information needed for the replication of cells.

Flagellum The flagellum has a rigid corkscrew shape and a rotating base to help the bacteria cell swim through fluids. The flagellum aids the movement of the cell.

This table compares and contrasts prokaryotic and eukaryotic cells and explains how they are different from viruses:

Prokaryotic cells Eukaryotic cells Viruses

A prokaryotic cell such as a bacteria cell has no true nucleus, it just has a diffuse area of nuclear material without nuclear envelope. A eukaryotic cell such as an animal cell has a distinct nucleus with a nuclear envelope. Viruses do not have a nucleus or a nuclear envelope.

A prokaryotic cell has no nucleolus. A nucleolus is present in eukaryotic cells. A virus has no nucleolus.

Prokaryotic cells have circular strands of DNA but no chromosomes. Eukaryotic cells have chromosomes in which DNA is located. In viruses DNA is enclosed inside a coat of protein.

Prokaryotic cells have no membrane-bound organelles. Eukaryotic cells have membrane-bound organelles such as mitochondria. Viruses have no membrane-bound organelles.

A prokaryotic cell doesn’t have any chloroplasts however some cells such as bacteria cells have photosynthetic membranes. Chloroplasts are present in some eukaryotic cells such as plant and algae cells. Chloroplasts are not an organelle found in viruses.

Ribosomes are smaller in prokaryotic cells than eukaryotic cells. Ribosomes are larger in eukaryotic cells than prokaryotic cells. A virus doesn’t have any ribosomes.

A prokaryotic cell doesn’t have an endoplasmic reticulum or associated organelles lysosomes and Golgi apparatus. A eukaryotic cell contains endoplasmic reticulum, lysosomes and Golgi apparatus. Viruses don’t have an endoplasmic reticulum or associated organelles lysosomes and Golgi apparatus.

The cell wall in a prokaryotic cell is made out of peptidoglycan. Not every eukaryotic cell has a cell wall, but the cells which do often have cell walls made mostly out of cellulose, fungi or chitin. Viruses don’t have a cell wall just a protein coat.

Task 3

This figure shows the fluid-mosaic model of the cell-surface membrane:

A) Glycoprotein

B) Sugar molecule

C) Phospholipid bilayer

D) Extrinsic protein molecule

E) Hydrophilic heads of phospholipid molecules

F) Intrinsic protein molecule

G) Cholesterol

H) Hydrophobic tails of phospholipid molecules

I) Glycolipid

The structure of the cell membrane is made up of many molecules. The glycoprotein are proteins with carbohydrate groups attached to them, glycoproteins act as recognition sites, as do glycolipids. The phospholipid bilayer is a fat based molecule made up of hydrophilic heads that point outwards and hydrophobic tails that point inwards. Protein molecules transport molecules across the membrane, some protein molecules are part of the internal structure (intrinsic) whilst others are placed outside of the body of the membrane (extrinsic). Carbohydrates add strength, limiting the movement of the phospholipid.

This structure is known as the fluid-mosaic model for the following reasons:

• Fluid because each individual phospholipid molecule has the ability to move relative to another. This provides the membrane with a flexible structure that is continually altering its shape.

• Mosaic because the proteins embedded in the phospholipid bilayer differ in pattern, shape and size just like the stones or tiles of a mosaic.

Comparison of the mechanisms of movement of molecules through cell membranes

Simple Diffusion Facilitated Diffusion Active Transport Cytosis

Type of membrane molecule involved

Phospholipids

Proteins

Proteins

Phospholipids

Force driving the process

Passive

Passive

Active

Active

Direction of transport

High to Low

High to Low

Low to High

High to Low

Examples of molecules transported

Oxygen

Carbon Dioxide

Water

Ions

Glucose

Amino Acids

DNA

Task 4:

For DNA replication and transcription the following factors must be present, ATP, enzymes, a supply of free RNA nucleotides and a gene to act as a template. The letters A T C G represent the base sequence in a DNA molecule and make up the genetic code. Hydrogen bonds these bases together between strands, A will always go with T and G will always go with C. A DNA code is made up of a three bases and is known as a triplet code. Each DNA code makes up a specific amino acid. The triplet of bases on the DNA and mRNA is known as a codon and on tRNA it is known as an anti-codon.

The two main stages of protein synthesis are transcription and translation. Translation takes place in the nucleus. The gene coding for the protein needed untwists then unzips and the hydrogen bonds break. Free RNA nucleotides form complementary base pairs with one strand of DNA bases. Weak H-bonds then form between the pairs and sugar phosphate bonds form between the RNA nucleotides. The mRNA strand is synthesised and peels off the DNA before moving out of the nucleus into the cytoplasm.

Translation usually takes place on the ribosomes in the cytoplasm, it can also take place on the ribosomes studded within the surface of the rough endoplasmic reticulum.  Ribosomes are the sites of protein synthesis, the mRNA strand attaches to a ribosome. tRNA molecules then transport specific amino acids to the ribosome, each mRNA codon codes for a specific amino acid. The codons and anti-codons then match up and form complementary base pairs. Finally, peptide bonds form between the adjacent amino acids to form the protein.

Task 5:

1) Explain how animal cells use nutrients to provide energy for growth, movement, and cell division.

ATP (adenosine triphosphate), also known as the universal energy currency, is a small molecule that has 3 phosphate groups (P) attached to one adenosine molecule (Adenosine-P-P-P). During respiration, high energy C-OH, C-C and C-H bonds are broken. Lower energy bonds are then formed and the difference is released so it can be used to attach a P to Adenosine-P-P (ADP adenosine diphosphate), which makes ATP. When energy is required at another point in time, a cell can use the ATP to break of the phosphate molecule at the end. This releases 30.6J for every ATP, ADP + P, which is the energy needed. The more ATP used, the more energy that is released. The cell needs to possess mitochondria for aerobic respiration to occur.  

Glycolysis is the splitting of sugar, it forms pyruvic acid from glucose in the cytoplasm of a cell. Glucose is phosphorylated twice to make a 6C sugar phosphate, making the glucose more reactive. This leads to the 6 carbon sugar phosphate breaking down into two, 3-sugar phosphates. So far we have put 1 glucose (6C) molecule into glycolysis to get back 2 pyruvic acids (3C) and four ATP molecules, giving us a net gain of 2ATP.  

The Krebs cycle removes hydrogen from pyruvic acid in the matric of the mitochondria. Each acetyl-CoA (2C) combines with an oxaloacetic acid (4C) to make a 6C compound (citric acid). In a series of steps for each 6C compound, two carbon dioxide molecules are released and 1 ATP molecule is directly made. The 4C compound is regenerated so that the cycle can begin again with more molecules of acetyl-CoA. The 4C compound is regenerated by the removal of the two Cs in the 2 carbon dioxide molecules. Krebs cycle produces two ATP molecules directly as the 6C molecule is passed around twice.  

The electron transport chain uses hydrogen to produce ATP in the inner mitochondrial membrane. All the hydrogen from the reduced hydrogen carriers enter a chain of reactions, which leads to the yield of energy in the form of ATP. Each hydrogen atom is split into a hydrogen ion and an electron. The electron is the part that gets passed down the chain from carrier to carrier and the hydrogen ion remains in the mitochondrial matrix. The electron carriers are at successively lower energy levels, we can tell this because as the electron moves on from one carrier to the next some energy is released. Per glucose molecule 38 molecules of ATP are produced.

2) Answer the following questions:

a) What is a tissue?

A group of cells which have a similar structure and function are called tissue.  There are four main types of tissue within the human body, these include:

• Epithelial tissue

Epithelia are the linings of external and internal surfaces and body cavities, including ducts (channels or tubes) carrying secretions from glands. They are composed of several layers of cells, called compound epithelia, or a single layer known as simple epithelia. The bottom or lowest layer of cells is attached to the basement membrane to provide support and connection. Some parts of the basement membrane can be secreted by the epithelial cells. There are nerve supplies to the epithelia but they're supplied with nutrients and oxygen from deeper tissues by diffusion. The surface tissues are often exposed to friction, therefore, the capacity for growth and repair is much greater than other tissues and this normally occurs during sleep.

Simple Epithelia:

Simple epithelial cells may be cuboidal, ciliated, columnar or squamous.

• Squamous epithelial cells are very flat and each nucleus forms a lump at the centre. The cell is very flat and fits together with other cells very closely. As they are so thin and delicate they don't offer much protection.

• Cuboidal epithelial cells have a spherical nuclei and are cube-shaped. This allows material to pass through in a similar way to diffusion and they often line ducts and tubes.

• Columnar epithelial cells have a slightly oval nuclei and are much taller than other simple epithelia. They are often associated with cilia and are then named ciliated epithelia.

Compound Epithelia:

The function of compound epithelia is to provide protection to deeper structure. Compound epithelia has multiple layers of cells. The vagina, tongue, oesophagus and mouth are lined by cells that are superficial and not keratinised. The skin is built up of outermost cells that have died and become hard due to deposition of keratin.

Simple squamous epithelium

 Simple cuboidal and columnar epithelial

 Section through stratified epithelium

• Connective tissue

Blood – Blood is a liquid matrix with flowing red and while cells that is found in the blood vessels.

Cartilage – Cartilage is a flexible but hard bone structure found in the nose, external ear and surface of bones.

Bone – Bones are hard calcified background materials in which various types of cell lie arranged osteons and found in the skeleton.

Areolar tissue – These are loose arrangements of cells and fibres found in the areas between organs and tissues.

Adipose tissue (fatty tissue) – These are cells that contain large amount of fat compartments and lie under the skin and padding at various points.

Types of connective tissues

• Muscle tissue

Striated muscle - Striated muscle is attached to the skeleton and has light and dark striations. This type of muscle is voluntary and the fibres develop tension and produce the movement by pulling on the bones.

Non-striated muscle - Non-striated muscle is found in the digestive tracts and blood vessels. This type of muscle, like cardiac muscle, is involuntary. It contracts in a wave like manner to pass content through the tubes, this is called peristalsis.

Cardiac muscle - Cardiac muscle is found in the walls of the heart and we have not conscious control over it. The muscle must keep contracting to enable our heart to keep pumping. The cardiac muscle is like skeletal muscle in appearance and is highly resistant to fatigue.

Striated muscle

Non-striated muscle

Cardiac Muscle

• Nervous tissue

Nervous tissue is only found in the nervous system and consists of the spinal cord, brain and nerves.

The nervous tissue is composed of two substances:

• Neurones – highly specialised cells that transmit the nervous impulses and are only present in the brain and spinal cord but their nerve fibres form the nerves.

• Neuroglia – connective tissue that is intermingled with neurones in the spinal cord and brain to offer support and protection.

General features of a neurone

b) What are stem cells?

Stem cells are unspecialised cells that have the potential to reproduce, differentiate and mature into a diverse range of specialised cells. A stem cell is capable of dividing an indefinite number of times. There are three different types of stem cell, these are, ‘adult’ stem cells (multipotent), embryonic stem cells (pluripotent) and lineage specific stem cells (unipotent).

c) What is meant by ‘cell differentiation’?

Initially all cells in an organism are identical. As the organism matures, each cell will take on its own specialist characteristics that suit the function it will be needed for when it’s fully matured. This is known as cell differentiation.

d) What is the purpose of cell differentiated cells?

Cell differentiation is important because it provides organisms with the different specialised cells needed to perform specific functions.

e) How do stem cells differ from differentiated cells?

Most animal cells differentiate at an early stage, and plant cells usually keep the ability to differentiate. The cells become specialised and can’t change into a different type of cell. Stem cells are different because they can be made to differentiate to form a different type of cell.

f) How are tissues formed from embryonic stem cells?

Embryonic stem cells are found in an embryo in its very first stages. The embryonic stem cells are usually taken from the embryo when it is blastocyst (4-5 days old). At this point the embryo has around 150 cells. These cells are pluripotent stem cells have the ability to differentiate into any cell type that makes up an organism.  The stem cells are then used to regenerate or repair diseased tissue and organs.

3) Explain the importance of interphase and the factors that initiate cell division.

Interphase is the longest stage of cell division, throughout this stage the cell is growing and preparing for replication. During interphase the cell has to make two of everything, this includes DNA which is does by protein synthesis and cell organelles such as mitochondria. In addition, the cell has to obtain and digest nutrition so it has the raw materials as well as the energy to power the cell during the duplication. During the process of duplication, the cells have to make sure there is going to be enough sufficient and accurate genetic material for each daughter cell. To ensure this the strands of DNA separate and attach to new strands. Due to the selectivity of the bases an exact replication of DNA occurs. As well as this, extra cell organelles are manufactured by the replication of existing organelles. Finally, the cell builds up and stores energy to be used during the process of cell division. Some factors that initiate cell division include, the death of nearby cells, the presence or absence of certain hormones, and cell growth.

4) Explain how the same genetic information is received by each daughter cell.

Every cell contains two sets of chromosomes which are homologous. However, they may be alternatives of the same gene. Mitosis begins by replicating DNA exactly. Once replicated, each chromosome becomes two identical chromatids joined at centromere. The chromosomes then become attached to a spindle - these are fibres that run from one pole to another. The individual chromosomes then line up at the equator of the cell. The centromere then divides and spindle fibres shorten to make each chromosome become two chromatids. Finally, the cell membrane ‘pinches in’ to separate the two sets of chromatids into two cells. The original cell has now become two daughter cells.

5) Compare and contrast cancer cells with normal cells.

A cancer cell is a cell which has a DNA mutation, normal cells will stop dividing if there is a mutation but cancer cells will continue to mutate. The cells continue to mutate because the DNA mutations make the cell unable to recognise the chemical signals that would usually stop and start the cell cycle. Cancer cells have a larger number of dividing cells compared to normal cells that divide through the controllable method of mitosis. The nuclei in cancer cells tend to have large variable shapes unlike normal cells which all have the same shape. Cancer cells also have a smaller cytoplasmic volume relative to the nuclei compared to normal cells. Healthy cells have the same overall size and shape unlike cancer cells which vary is shape and size. Cancer cells experience loss of normal specialised features and the arrangement of the cells often appears disorganised. Finally, cancer cells have a poorly defined tumour boundary.

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