Unit 3: Genome

Question 1

What are prokaryotes and eukaryotes?

Answer 1

Prokaryotic organisms have prokaryotic cells (they are singled celled organisms). They are smaller and simpler (like bacteria), compared to Eukaryotic (contain eukaryotic cells), which are complex and include animal and plant cells.
Both types of cells contain organelles (parts of the cells) and each one has a special function. If you examine through a light microscope you can see its organelles and the internal structure of most of them (cell ultrastructure)

Question 2

Description and explain the function the nucleus.

Answer 2

A large organelle surrounded by a nuclear envelope (double membrane), which contains many pores. The nucleus contains chromatin (which is made from DNA and proteins) and the structure is called the nucleolus.
It controls the cells’ activities by controlling the transcription of DNA. The DNA contains instructions about how to make proteins. The pores allow substances (like RNA) to move between the nucleus and the cytoplasm. The nucleolus makes ribosomes.

Question 3

Describe and explain the function of the lysosome

Answer 3

It is a round organelle that is surrounded by a membrane, with no clear internal structure.
It contains digestive enzymes. These are kept separate from the cytoplasm by the surrounding membrane, and can be used to digest invading cells or to break down worn out components of the cell

Question 4

Describe and explain the function of the ribosome

Answer 4

It is a very small organelle that either floats free in the cytoplasm or is attached to the rough endoplasmic reticulum. It is made up of proteins and RNA. It’s not surrounded by a membrane. Usually pictured as a dot.
This is the site where proteins are made.

Question 5

Describe and explain the function of rough endoplasmic reticulum (RER)

Answer 5

A system of membranes enclosing a fluid-filled space. The surface is covered in ribosomes.
Folds and processes proteins that have been made at the ribosomes.

Question 6

Describe and explain the function of smooth endoplasmic reticulum (SER)

Answer 6

Similar to rough endoplasmic reticulum, but has no ribosome.
It is used to synthesises and process lipids.

Question 7

Describe and explain the function of Golgi apparatus

Answer 7

A group of fluid-filled, membrane-bound, flattened sacs. Vesicles are often found at the edges of the sacs.
It is used in the process and packaging of new lipids and proteins and it also makes lysosomes.

Question 8

Describe and explain the function Mitochondrion

Answer 8

They are usually oval-shaped. They have a double membrane, the inner one is folded to form structures called cristae. Inside is the matrix, which contains enzymes involved in respiration.
It is the site of aerobic respiration where ATP is produced. They’re found in large numbers in cells that are very active and require a lot of energy.

Question 9

How are organelles involved in protein production and transport

Answer 9

1) Proteins are made at the ribosome.
2) The ribosome at the rough endoplasmic reticulum (RER) make proteins that are excreted or attached to the cell membrane. The free ribosomes in the cytoplasm make proteins that stay in the cytoplasm.
3) New proteins produced on the rough ER are folded and processed (e.g. sugar chains are added) in the rough ER.
4) Then they are transported from the ER to the Golgi apparatus in vesicles.
5) At the Golgi apparatus, the proteins may undergo further processing (e.g. sugar chains are trimmed or more added to)
6) The proteins enter more vesicles to be transported around the cell. (E.g. extracellular enzymes - like digestive enzymes - more to the cell surface to be secreted)

Question 10

The structure of prokaryotes and how they are different to eukaryotes (no membrane bound, plasma, support, hair-like structures, protection)

Answer 10

• The cytoplasm of prokaryotic cells has been no membrane-bounded organelles (unlike eukaryotic cells). It has ribosomes but they are smaller than the ribosomes in eukaryotic cells.
• Similar with eukaryotic cells, the plasma membrane is mainly made up of lipids and proteins. It controls the environment of substances into and out of the cell.
• The cell wall supports the cell and prevents is from changing shape. It is made from a polymer called murein (a glycoprotein- proteins with a carbohydrate attached)
• Some prokaryotes have short hair called pili, this helps prokaryotes to stick to other cells and can be used to transfer genetic material between cells.
• Some, like bacteria, have a capsule made up of secreted slime. It helps to protect bacteria from attacks by cells of the immune system.

Question 11

The structure of prokaryotic cells and how they are different to eukaryotic cells (inward folds, plasmids, nucleus, movement)

Answer 11

• Mesosomes are inward folds in the plasma membrane. Scientists are still debating what their function is. Some believe they play a role in cellular processes. However, other believe that they’re not natural features at all and are just artefacts produced when the cells are being prepared to be viewed under the microscope.
• Plasmids are small loops of DNA that aren’t part of the main circular DNA. They contain genes for processes like antibiotic resistance, and can be passed between prokaryotes. Not always present, some have several.
• Doesn’t have a nucleus but instead the DNA floats free in the cytoplasm. Circular DNA, present as one long coiled-up strand. It’s not attached to any histone proteins.
• Flagellum (plural flagella) is a long-hair-like structure that rotates to make the prokaryote cell move. Not all have this, some have several

Question 12

What is magnification and resolution?

Answer 12

Magnification is how much bigger the image is than the specimen. Calculated with the formula:
magnification= size of image/size of real object
Resolution is how detailed an image is. More specifically it’s how well a microscope distinguishes between two points close together. If a microscope lens can’t separate two objects, then increasing the magnification won’t help.

Question 13

What is a light microscope?

Answer 13

They use light to form an image. They have a maximum resolution of about 0.2 micrometres. This means you can’t see a light microscope to view organelles smaller than 0.2 micrometres. That includes ribosomes, the endoplasmic reticulum and lysosomes. You may be able to see the mitochondria but not in perfect detail and you can see the nucleus. The maximum useful magnification of a light microscope is about x1500.

Question 14

What is an electron microscope?

Answer 14

They use electrons to form an image. They have a higher resolution than a light microscope so give a more detailed image and so they can be used to look at more organelles. They have a maximum resolution of about 0.0002 micrometres (1000 times higher than a light microscope). The maximum useful magnification of an electron microscope is about x 1,500,000.

Question 15

What is a transmission electron microscope?

Answer 15

Transmission electron microscope (TEMs) use electromagnets to force a beam of electrons, which is then transmitted through specimen. Denser parts of the specimen absorb more electrons, which makes them darker on the image you end up with. TEMs are good because they give high resolution images. so you see the internal structures of organelles like mitochondria. Only used on thin specimen.

Question 16

Scanning electron microscopes

Answer 16

Scanning electron microscopes (SEMs) scan beam of electrons across the specimen. This knocks off electrons from the specimen, which are gathered in the cathode ray tube to form an image. The images you end up with show the surface of the specimen and they can be 3D. SEMs are good because they can be used on thick specimen, but have a lower resolution than TEMs.

Question 17

What is a tissue?

Answer 17

It is a group of similar cells that are specially adapted to work together to carry out a particular function. For example, Squamous epithelium (single layer of cells, found in many places including the alveoli in the lungs), ciliated epithelium (tiny layer that covers the cilia and is found in surfaces that need to be moved- trachea-mucus), xylem tissue (transports water and supports the plant) and cartilage (connective tissue in the joints- shapes and supports the ears, nose and widepipe)

Question 18

What is an organ?

Answer 18

It is a group of different tissue that work together to perform a particular function. Leaf- lower epidermis (contains stomata - holes- to let air in and out for gas exchange for gas exchange), spongy mesophyll (full of spaces to let gases circulate), palisade mesophyll (most photosynthesis occurs here), xylem (carries water to the leaf), phloem (carries sugar away from the leaf), and upper epidermis (covered in a waterproof waxy cuticle to reduce water loss). Lungs- squamous epithelium tissue (surrounds the alveoli- where gas exchange occurs), fibrous connective tissue (helps to force air back out of the lungs when exhaling), and endothelium tissue (makes up the wall of the capillaries- surround the alveoli and lines the larger blood vessels).

Question 19

What different organs make different organ systems?

Answer 19

Respiratory system: lungs, trachea, larynx, nose, mouth and diaphragm.
Circulatory system: heart, arties, veins, and capillaries.

Question 20

What is mitosis?

Answer 20

A parents cell divides to produce two genetically identical daughter cells (contain an exact copy of DNA from parents cell). Mitosis is needed for the growth of multicellular organisms, for repairing damaged tissue, and for asexual reproduction. Not all cells keep their ability to divide, the ones that do follow the cell cycle. The cell cycle consists of a period of cell growth and DNA replication called interphase. Mitosis happens after interphase. Interphase is subdivided into 3 separate stages, called G1 (Gap stage 1- cell grows and new organelles and proteins are made), S (Synthesis- cell replicates its DNA, ready to divide by mitosis), G2 (Gap stage 2- cell keeps growing and proteins needed for cell division are made), then mitosis happens.

Question 21

What are the four stages of mitosis?

Answer 21

Interphase happens before mitosis. DNA is unravelled and replicated to double genetic content. The organelles are replicated so it has spare ones and its ATP content increased (provides energy for cell division).
1) Prophase- chromosomes condense (get shorter and fatter), centrioles start to move to opposite pole, forming a network of protein fibres (spindle), nuclear envelope breaks down and the chromosomes lie free in the cytoplasm.
2) Metaphase- Chromosomes line up in the middle of the cell and become attached to the spindle by the centromere.
3) Anaphase- Centromeres divide, separating each pair of sister chromatids. The spindles contract, pulling to opposite poles of the spindle, centromere first, chromatids appear V-shape.
4)Telophase- Chromatids reach the opposite poles on the spindle. They uncoil and become long and thin again (chromosomes again), nuclear envelope forms around each group of chromosomes so there is now 2 nuclei, cytoplasm divides (cytokinesis), now 2 daughter cells and are genetically identical. Ready for the next mitosis.

Question 22

Practical: Root tip (Mitosis)

Answer 22

1) Cut 1 cm from the tip from a growing root (where growth occurs-mitosis).
2) Prepare a boiling tube containing 1M hydrochloric acid and put it in water bath-60 degrees C.
3) Transfer the root tip into the boiling tube and incubate for 5 mins.
4) Use a pipette to rinse the root tip well with cold water. Leave to dry- paper towel
5) Place the root tip on a microscope slide and cut 2mm away from the very tip, get rid of the rest.
6) Use mounted needle to break the tip open and spread the cells out thinly.
7) Add a small drop of stain and leave it for a few mins- makes the chromosomes easier to see under microscope (ethano-orcein)
8) Place a cover slip over the cells and press down firmly to squash the tissue- make it thinner and allow light to pass through- don’t smear the cover slip.
9) Now look under the light microscope.

Question 23

What is the mitotic index?

Answer 23

Mitotic index= number of cells with visible chromosomes/ total number of cells observed.
This tells you how quickly the tissue is growing. Plant root tip is constantly growing, so you would expect a high mitotic index.

Question 24

How is DNA passed down to new offspring?

Answer 24

Gametes are male and female sex cells found in all organisms that reproduce sexually. Join together a fertilisation to form a zygote, which divides to create a new organism. Animals- male= sperm and female = egg cell (ova). Human have a full set of chromosomes- 2 sets (pairs) of 23 chromosomes- one set is from the male parent and the other from the female. Giving a total of 46 chromosomes. Gametes only contain half the number of chromosomes, only one set (23). Fertilisation creates a zygote with the full number of chromosomes. Fertilisation is used to describe the exact moment the nuclei of the male and female gamete fuse. Combing the genetic material from the two individuals makes the offspring genetically unique.

Question 25

How is mammalian gametes specialised?

Answer 25

They have the same organelles as other eukaryotic cells. But they have other features to make them specialised for their role.
Egg cell- cell (plasma) membrane. Follicle cells form protective coating. Zona pellucida- protective glycoprotein layer that sperm have to penetrate. Egg cells are much bigger than sperm cells. Egg cells contain huge food reserves to nourish the developing embryo.
Sperm cell- Lots of mitochondria to provide energy for tail movement. Nucleus, Cell (plasma) membrane, acrosome contains digestive enzymes to break down the egg cell’s zona pellucida and enable sperm to penetrate the egg. Flagellum (tail) allows sperm to swim towards egg cell.

Question 26

How does fertilisation occur in the oviduct?

Answer 26

1) In mammals, sperm are deposited high up in the female vagina close to the entrance of the cervix.
2) Once there, they have to make their way up through the cervix and uterus, and into one of the oviducts.
3) Once the sperm is there fertilisation can occur.

Question 27

How does fertilisation occur?

Answer 27

1) The sperm swims toward the egg cell in the oviduct.
2) One sperm will make contact with the zona pellucida of the egg cell, acrosome reaction can occur- digestive enzymes are released from the acrosome of the sperm.
3) The enzymes digest the zona pellucida, so that the sperm can move through it to cell membrane of the egg cell.
4) Sperm head fuses with the cell membrane of the egg cell. This triggers the cortical reaction- the egg cell releases the contents of vesicles called cortical granules into the space between cell membrane and the zona pellucida.
5) Chemicals from the cortical granules make the zona pellucida thicken, which makes it impenetrable to other sperm. This makes sure only one sperm fertilises the egg cell.
6) Nucleus of the sperm fuses with the nucleus of the egg cell (fertilisation)
The zygote is now formed with a full number of chromosomes and immediately begins to divide by mitosis to develop into a fully formed organism.

Question 28

How does the cell divide to produce gametes?

Answer 28

Meiosis is the cell division that happens in reproductive organs to produce gametes. Cells that divide by meiosis have a full number of chromosomes to begin with, but the cells that have formed from meiosis have half the number. Without meiosis you would have double the number of chromosomes when the gametes fused for fertilisation.

Question 29

Brief overview of meiosis

Answer 29

1) The DNA replicates so there are two identical copies of each chromosome, called chromatids.
2) The DNA condenses to form double-armed chromosomes, made from sister chromatids.
3) The chromosomes arrange themselves into homologous pairs - pairs of matching chromosomes (one from each set of 23- e.g. both number 1s)
4) First division- the homologous pairs are separated, having the number of chromosomes.
5) Second division- the pairs of sister chromatids are separated.
6) 4 new daughter cells that are genetically different from each other are produced. These are gametes.

Before being pulled apart in cell division 1 and 2 they always line up at the equator of the cell and then after being pulled apart (pulled to the poles) the cell pinches in the middle to give a new cell.

Question 30

How does meiosis produce cells that are genetically different? (crossing over chromatids)

Answer 30

1) Before the first division of meiosis, the homologous pairs of chromosomes come together and pair up.
2) Two of the chromatids in each homologous pair twist around each other
3) The twisted bits break off their original chromatid and re-join onto the other chromatid, recombing genetic material.
4) The chromatids still contain the same genes but they now have different combination of alleles.
5) This means that each of the four new cells have formed from meiosis contains chromatids with different alleles.

Question 31

How does meiosis produce cells that are genetically different?

Answer 31

1) The four daughter cells formed from meiosis have completely different combinations of chromosomes.
2) All your cells have a combination of chromosomes from your parents, half mum (maternal) and half dad (paternal).
3) When the gametes are produced, different combinations of those material and paternal chromosomes go into each cell.
4) This is called independent assortment (separation) of the chromosomes.

Question 32

How are some genes sex linked?

Answer 32

The position of a gene on a chromosome is called the locus. Independent assortment means that genes with a loci on a different chromosome end up randomly distributed in the gametes.
But genes with loci on the same chromosome are said to be linked- because the genes are on the same chromosome, they’ll stay together during independent assortment and their alleles will be passed on to their offspring together. The only reason this won’t happen is if crossing over splits them up first.
The closer together the loci of two genes on a chromosome, the more likely they are said to be linked. This is because crossing over is less likely to split them up.

Question 33

How are some characteristics sex-linked?

Answer 33

1) A characteristic is said to be sex-linked when the locus of the allele that codes for it’s sex chromosome.
2) In mammals, females have two X chromosomes (XX) and males have one X and one Y (XY).
3) The Y chromosome is smaller and carries fewer genes. So most of the genes on the sex chromosome are only carried on the X chromosome (X-linked genes)
4) As males only have one X chromosome, they often only have have one allele for sex-linked genes. So because they only have one copy, they express the characteristics of this allele even if it’s recessive. This makes males more likely than females to show recessive phenotype for genes that are sex-linked.
5) Genetic disorders caused by faulty alleles on sex chromosomes include colour blindness and haemophilia, Both of these are disorders carried by the X-chromosome (X-linked disorders)

Question 34

How are stem cells able to differentiate into specialised cells?

Answer 34

Specialised cell types originally come from stem cells. Stem cells are unspecialised cells that have developed into other types of cells. Stem cells divide by mitosis to become new cells, which then become specialised. The process at which cells become specialised is called differentiation. All multicellular organisms have some form of stem cell. Human stems cells are found in embryo. The ability of stem cells to differentiate into specialised cells is called potency (Totipotency, pluripotency). Stem cells can also be found in some adults tissue- specialised to be replaced- less flexible and can only develop into some cell types. Plants also have stem cells found in areas where the plant is growing- roots and shoots.

Question 35

What is the difference between totipotency and pluripotency?

Answer 35

Totipotency is the ability to produce all cell types, including all specialised cell in an organism and extraembryonic cells (cells of the placenta and umbilical cord). Only present in mammals in the first few cell divisions of an embryo. Embryonic stem cells become pluripotent, they can become any cell in the body, but lose the ability to become cells that make up the placenta and umbilical cord.
Pluripotency is the ability of a stem cell to produce all the specialised cells in an organism, but not the extraembryonic cells, as the genes for these cells has become inactive.

Question 36

How does different gene expression cause stem cells to become specialised?

Answer 36

1) Stems cells contain the same genes, but not all of them are expressed because not all of them are active.
2) Under the right conditions, some genes are activated and the others inactivated.
3) mRNA is only transcribed from the active genes.
4) mRNA from the active gene is then translated into proteins
5) These proteins modify the cell- they determine the cell structure and control cell processes - including the activation of more genes.
6) Changes to the cell produced by these proteins causes the cell to become specialised (differentiate). These changes are difficult to reverse, so once the cell is specialised, it stay specialised.
Example: Red blood cell contains lots of haemoglobin and have no nucleus. Produce a type of stem cell in the bone marrow. Produces a new cell which genes for haemoglobin production is activated. Other genes like removing nucleus are activated.

Question 37

How can transcription factors control the expression of genes?

Answer 37

Gene expression can be controlled by altering the rate of transcription genes- increase transcription produces more mRNA, which can be used to make more protein. This is controlled by transcription factors- proteins that bind to the DNA and active or deactivate genes by increasing or decreasing the rate of transcription. Increase rate of transcription= activators (helping RNA polymerase bind to DNA and begin transcription) and those that decrease rate of reaction= repressors (prevent RNA polymerase from binding and so stopping transcription. Eukaryotes (plant and animals)- transcription factor bind to specific DNA sites near control of the gene expression often involves transcription factors binding to operons.

Question 38

An operon is a section of DNA that contains a cluster of structural genes, that are transcribed together, how does it control elements and sometimes regulatory gene?

Answer 38

• Structural genes code for useful proteins, such as enzymes.
• The control elements include a promoter (DNA sequence located before the structural genes that RNA polymerase binds to) and an operator (a DNA sequence that transcription factors bind to).
• The regulatory gene codes for an activator or repressor.

Question 39

What happens with lac operon in E.coli?

Answer 39

E.coli is a bacterium that respires glucose, but it can use lactose if glucose isn’t available. The genes are produced are the enzymes needed to respire lactose are found on an operon called lac operon. It has 3 structural genes- lacZ, lacY, and lacA, which produce proteins that help the bacteria to digest lactose (including beta-galactosidase and lactose permease)

Question 40

What happens when lactose is not present?

Answer 40

The regulatory gene (lacl) produces lac repressor, which is a transcription factor that binds to the operator site when there’s no lactose present. This blocks transcription because the RNA polymerase can’t bind to the promoter.

Question 41

What happens when lactose is present?

Answer 41

When lactose is present, it binds to the repressor, changing the repressor’s shape so that it can no longer bind to the operator site. RNA polymerase can now begin transcription of the structural genes.

Question 42

How can stem cells be used to treat some diseases?

Answer 42

Stem cells develop into any specialised cell to replace damaged tissue in a range of diseases. Some stem cell therapies already exist like to treat leukaemia- which kills stem cells in the bone marrow, so there is a bone marrow transplant to replace them. Spinal cord injuries could use stem cells to repair damaged nerve tissue. Heart disease and damage caused by heart attacks, stem cells used to replace heart tissue. Potential benefits- they could save many lives, many people who are waiting for a transplant die before getting the organ. -They could improve the quality of life in so many people- replace cells in the eye for blind people.

Question 43

How could we source stem cells from adults?

Answer 43

From body tissue of an adult, like bone marrow. Simple operation with a very little risk but a lot of discomfort. Donor is anaesthetised, a needle is inserted into the centre of the bone. They aren’t as flexible as embryonic stem cells- limited range of cells. If the stem cells come from the patient there is a less risk of rejection.

Question 44

How could we source stem cells from embryos?

Answer 44

You need an early embryo, created in a laboratory using in vitro fertilisation (IVF)- fertilisation outside the womb. 4 to 5 days old, stem cells are removed and the rest of the embryo is destroyed. Develop into all specialised cells.

Question 45

Ethical issues from obtaining stem cells from embryos.

Answer 45

Many people believe it has a right to life- it is wrong to destroy the embryo. However, some people have fewer objections to stem cells that have been artificially activated to start dividing. Cells wouldn’t survive past a few days and wouldn’t produce a foetus if placed in a womb. Only use adults- doesn’t destroy the embryo, but can’t specialise into all cell types.

Question 46

How could society make decisions whether to use embryonic stem cells?

Answer 46

Proposal of the research (good reason). Licensing and monitoring centres with fully trained staff. Guide lines and codes of practice. Monitoring developments. Providing information and advice to governments and professionals

Question 47

What is continuous variation?

Answer 47

Individuals in a population vary within a range- there are no distinct categories like height, mass, skin colour.

Question 48

What is discontinuous variation?

Answer 48

When there are two or more distinct categories- individuals only fall into one category like blood group.

Question 49

How does variation in genotype influence variation in phenotype?

Answer 49

Individuals of the same species have different genotypes (combination of alleles). Variation in genotype results in variation in phenotype- characteristics displayed. Some characteristics are controlled by one gene- monogenetic (discontinuous variation- blood group). Most characteristics are controlled by a number of genes at different loci- polygenetic (continuous variation)

Question 50

How does the environment influence genotype?

Answer 50

Height is polygenetic- nutrition (undernourishment won’t achieve their maximum height) Monoamine Oxidase A (MAOA) is an enzyme that breaks down monoamines (chemical) in humans. Low levels of MAOA linked to mental health problems. Production is controlled by a single gene (monogenetic) but taking anti-depressants or smoking tobacco can reduce the amount that is produced. Cancer is uncontrolled cell division that leads to lumps of cells (tumours) - genes and environment like smoking and diet. Animal hair colour is polygenetic, but the environment plays a part in some animals like heat. Himalayan rabbit extremities are black and the body is white, as the gene inactive on the main body but is making it black on the extremities as the enzyme is active (active at 35 degrees C- cool enough)

Question 51

How can changes in the environment cause changes to gene expression?

Answer 51

Eukaryotes, epigenetic control can determine whether certain genes are expressed, altering the phenotype. Epigenetic control doesn’t alter the base sequence of DNA. It works by attaching or removing chemical groups to and from the DNA. This is alters how easy it is for the enzymes and other proteins needed for transcription to interact and transcribe genes. Epigenetic changes to gene expression [play a role in lots of cellular processes. They can also occur in response to changes in the environment- like pollution

Question 52

What happen if you increased the methylation of DNA represses a gene?

Answer 52

One method for epigenetic control is methylation of DNA- this is when a methyl group is attached to the DNA coding for a gene, The group always attaches at a CpG site, which is where a cytosine and guanine base are next to each other in the DNA. Increased methylation changes the DNA structure, so that proteins and enzymes needed for transcription can’t bind to the gene- so the gene is not expressed (repressed or inactive)

Question 53

How can modification of histones also affect gene expression?

Answer 53

Histones are proteins that DNA wraps round to form chromatin, which make up chromosomes. It can be highly condensed or less condensed. How condensed it is affects the accessibility of the DNA and whether or not the proteins and enzymes needed for transcription can bind to it.
Epigenetics modifications to histones include the addition or removal of acetyl groups:
- Histones are acetylated, the chromatin is less condensed- proteins involved in transcription can bind to the DNA, allowing genes to be transcribed (activated)
- Acetyl groups removed (from histone)- chromatin becomes highly condensed and the genes in the DNA can’t be transcribed because the transcription proteins can’t bind to them- the genes are repressed.

Question 54

How can epigenetics be passed on after cell division?

Answer 54

Cell divides and replicates- epigenetic changes to its gene expression may be passed on to the resulting daughter cells. If epigenetic changes get passed on, it means that certain genes that are activated or deactivated in the original cell will also be activated or deactivated in the daughter cells. If epigenetic changes happen in a response to a change in the environment, this means that the daughter cells will be equipped to deal with the changed environment in the same way the original cell was.