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Biology: Paper 1 > Module 2: cell division, cell diversity + organisation. > Flashcards

Module 2: cell division, cell diversity + organisation. Flashcards

1
Q

What is the cell cycle?

A

It is the process that all body cells in multicellular organisms use to grow and divide.

It starts when a cell has been produced by cell division and ends with the cell dividing to produce two identical cells.

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2
Q

What does interphase consist of?

A

Interphase: It is made up of three growth phases called G1 phase, S phase and G2 phase.

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3
Q

What happens in GAP PAHSE 1 and its checkpoint?

A

GAP PHASE 1: The cell grows and new organelles and proteins are made.

G1 checkpoint: The cell checks that the chemicals needed for replication are present and for any damage to the DNA before entering S-phase.

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4
Q

What happens at the SYNTHESIS stage? (S)

A

The cell replicates its DNA and is ready to divide by mitosis.

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5
Q

What happens at the GAP PHASE 2 and its checkpoint?

A

GAP PHASE 2: The cell keeps growing and proteins needed for cell division are made.

G2 Checkpoint: The cell checks whether all the DNA has been replicated without any damage. If it has, The cell can enter mitosis.

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6
Q

What happens in M phase?

A

This consists of Mitosis and Cytokinesis.

Mitosis: is a type of cell division where cells produce identical copies of themselves and is used for growth and repair and asexual reproduction.

Cytokinesis: it is the final step of mitosis, where the cell will completely divide in two identical daughter cells as the cytoplasm + cell membrane separates.

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7
Q

What is the structure of chromosomes in Mitosis?

A

As mitosis begins, the chromosomes are made of two strands joined in the middle by a centromere.

The separate strands are called Chromatids.

Two strands on the same chromosome are called sister chromatids.

There are two strands because each chromosome has already made an identical copy of itself during interphase. When mitosis is over, the chromatids end up as one-strand chromosomes in the new daughter cells.

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8
Q

What are the stages of Mitosis called?

A

1) Prophase
2) Metaphase
3) Anaphase
4) Telophase

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9
Q

Explain what happens in Prophase.

A

The chromosomes condense (they become shorter and fatter)

The centrioles move to opposite poles of the cell and form spindle fibres.

The nuclear envelope breaks down and the chromosomes lie free in the cytoplasm.

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10
Q

Explain what happens in Metaphase.

A

The chromosomes line up along the middle of the cell.

They attach to the spindle fibre by their centromere.

At the metaphase checkpoint, the cell checks that all the chromosomes are attached to the spindle before mitosis can continue.

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11
Q

Explain what happens in Anaphase.

A

The centromere divides, separating each pair of sister chromatids.

The spindles contract and the sister chromatids are pulled to opposite poles of the cell - centromere first.

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12
Q

Explain what happens in Telophase.

A

The chromatids reach the opposite poles on the spindle.

The two groups of chromosomes decondense (they become long and thin) and a nuclear envelope reforms around them, forming two new nuclei.

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13
Q

Explains what happens in cytokinesis.

A

The cytoplasm divides.

In animal cells, a cleavage furrow forms to divide the cell membrane.

There are now two daughter cells that are genetically identical to the original cell and to each other.

Usually begins in anaphase and ends with telophase and it is a separate process to mitosis.

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14
Q

Describe the practical investigating mitosis in squashed root tips.

A

Cut a thin section of tissue from the tip of a growing root.

Pipette a set volume of 1M hydrochloric acid into a boiling tube and place in a 60oC water bath.

Place the plant tissue in the boiling tube and leave for five minutes.

Rinse the root tip with cold water and dry using a paper towel.

Cut the root tip so that you have a thin layer of cells (about 2 mm) and spread out onto a microscope slide using a mounted needle.

Add a drop of Toluidine blue O stain to the tissue and place a cover slip on top. Push down on the cover slip to squash the cells and allow light to pass through. Be careful not to push sideways otherwise the chromosomes will become damaged.

Use a light microscope to visualise the cells and identify the stages of mitosis. Any cells with visible chromosomes will be undergoing mitosis (as the chromosomes are condensed).

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15
Q

What are gametes?

A

Gametes are sex cells (the sperm and egg in humans).

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16
Q

What is sexual reproduction?

A

This is when two gametes (
sperm/egg cell) join together at fertilisation to form a zygote, which divides and develops into a new organism.

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17
Q

What does haploid and diploid mean?

A

Gametes are haploid which means they contain half the number of chromosomes as the rest of the cells which make up our body.

This means that when two gametes fuse during sexual reproduction, the fertilised egg (called a zygote) contains the full number of chromosomes i.e. it is diploid.

In humans, the diploid number of chromosomes is 46 (23 pairs), which means that gametes contain just 23 chromosomes.

During sexual reproduction, the nucleus of the sperm cell fuses with the nucleus of the egg cell - this fusion of nuclei is called fertilisation.

This forms a Diploid zygote which continues to divide to form an embryo

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18
Q

What is Meiosis?

A

It is a type of cell division that happens in the reproductive organs to produce gametes for sexual reproduction.

Cells that divide by meiosis are diploid to start with, but the cells that are formed from meiosis are haploid- the chromosomes number halves.

Cells formed by meiosis are all genetically different because each new cell ends up with a different combination of chromosomes.

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19
Q

How much divisions does meiosis have?

A

It involves 2 divisions- meiosis 1 and meiosis 2.

After interphase, the cells enter meiosis 1.

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20
Q

What happens in Interphase before Meiosis 1?

A

The whole of meiosis begins with interphase.

During interphase, the cells DNA unravels and replicates to produce double-armed chromosomes called sister chromatids.

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21
Q

What are the stages of Meiosis 1?

A

Prophase 1

Metaphase 1

Anaphase 1

Telophase 1

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22
Q

What happens in Prophase 1?

A

The chromosomes condense getting shorter and fatter.

Homologous chromosomes pair up and crossing over occurs.

The centrioles start moving to opposite ends of the cell, forming the spindle fibres.

The nuclear envelope, the membrane around the nucleus, starts to break down.

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23
Q

What happens in Metaphase 1?

A

The homologous pairs line up across the centre of the cell (equator) and attach to the spindle fibres by their centromeres.

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24
Q

What happens in Anaphase 1?

A

The spindles contract, pulling the pair apart- one chromosome goes to each end of the cell.

25
Q

What happens in Telophase 1?

A

A nuclear envelope forms around each group of chromosomes.

Cytokinesis (division of the cytoplasm) occurs and two haploid daughter cells are produced.

26
Q

What happens after Meiosis 1 is complete?

A

The two daughter cells formed from Meiosis 1 undergo prophase 2, metaphase 2, anaphase 2, telophase 2 and cytokinesis.

27
Q

Describe the stages of Meiosis 2.

A

Prophase II: chromosomes condense, nuclear envelope disintegrates and spindle fibres form.

Metaphase II: chromosomes attach to the spindle fibre by their centromeres.

Anaphase II: sister chromatids are separated. Each new daughter cell inherits one chromatid from each chromosome

Telophase II: chromatids reach opposite poles of the cell. Nuclear envelope reforms and cytokinesis takes places. Four genetically unique daughter cells are produced.

28
Q

What does genetic variation mean?

A

It is the differences that exist between individuals’ genetic material.

29
Q

Why is genetic variation important?

A

It makes gametes that are all genetically different. Then during fertilisation, any egg can fuse with any sperm, which also creates variation. This means new individuals have a new mixture of alleles, making them genetically unique.

If everyone had similar genes, they would all be equally vulnerable to the same diseases and other threats to their survivals.

30
Q

What are the 2 ways that lead to genetic variation?

A

Crossing over

Independent assortment.

31
Q

What is crossing over?

A

During prophase I of meiosis, a process called crossing over occurs. This is when the homologous chromosomes move towards each other and exchange genetic material.

A chromatid from the maternal chromosome becomes twisted around the paternal chromosome and they connect through a structure called the chiasmata.

Pieces of chromosomes are exchanged and the chromatids separate, forming chromosomes with different combinations of alleles.

32
Q

What is Independent assortment?

A

Depending on the order in which chromosomes line up along the equator of the cell during metaphase, different combinations of chromosomes will end up in each gamete.

The way in which the chromosomes align themselves on the spindle fibre is completely random, resulting in a huge number of possibilities of chromosomal combinations in the gametes.

33
Q

What are stem cells?

A

They are unspecialised cells that can develop into different types of cell.

Stem cells have an unlimited capacity to divide and can produce lots more stem cells by mitosis- renew themselves.

34
Q

Where are stems cells found?

A

Found in early embryos

Found in bone marrow in adults.

35
Q

What does cell differentiation mean?

A

It is the process by which a cell becomes specialised for its job.

36
Q

What is potency?

A

It is the ability of stem cells to undergo differentiation.

37
Q

What are the different levels of potency?

A

Totipotent - totipotent cells have the ability to divide into any type of cell (including the extra-embryonic cells which make up the placenta and umbilical cord).

Pluripotent - pluripotent cells can divide into any type of cell except the extra-embryonic cells.

Multipotent - these cells can divide into a handful of different cell types

Unipotent - these cells can only divide into one type of cell

38
Q

What is the difference in stem cells in humans and plants?

A

Adult bone marrow contains multipotent adult stem cells which can divide and differentiate to replace old blood cells. They are responsible for forming all the different types of red and white blood cells.

In plants, stem cells are present in regions called meristems, found at the tip of the shoot and roots. These have greater potency than adult stem cells, and can divide to form almost any kind of cell.

39
Q

Why are stem cells important in medicine?

A

They have a huge potential for use in medicine as they can develop into different specialised cell types.

Scientists thinks that they could be used to repair damaged tissues (like the heart) and treat neurological disorders such as Alzheimer’s and Parkinson’s.

Studying stem cells can help us to understand more about things like developmental disorders and cancer.

40
Q

Give examples on how stem cells are being used as a treatment for certain diseases.

A

Stem cell transplants are given to patients with leukaemia - leukaemia is a type of cancer which destroys stem cells so bone marrow transplants are used to replace the lost stem cells.

Research is being carried out to develop ways of growing whole organs from stem cells. The organs can then be transplanted into the patient to replace organs that have been damaged or are diseased e.g. pancreatic transplants can be given to people with diabetes. This approach will help those who currently have to wait years for an organ donation.

Parkinson’s- stems cells used to regenerate dopamine producing cells.

41
Q

How are Erythrocytes specialised for their functions?

A

These are red blood cells that carry oxygen in the blood.

The biconcave disc shape provides a large surface area to gas exchange.

They have no nucleus so there is more room for haemoglobin.

42
Q

How are Neutrophils specialised for their functions?

A

They are a type of white blood cell that defends the body against disease.

Their flexible shape allows them to engulf foreign particles/pathogens.

They have lots of lysosomes in their cytoplasm that contains digestive enzymes to break down the engulfed pathogen/particle.

43
Q

How are Epithelial cells specialised for their functions?

A

They cover the surface of organs.

The cells are joined by interlinking cell membranes and a membrane at their base.

Ciliated epithelia’s (in airways) have cilia that beat to move particles away.

Other epithelia’s (in the small intestine) have microvilli- folds in the cell membrane that increase the cells surface area.

Squamous epithelia (in the lungs) are very thin to allow efficient diffusion of gases.

44
Q

How are sperm cells specialised for their functions?

A

They are male sex cells that have a flagellum (tail) so they can swim to the egg.

They have lots of mitochondria to provide energy to swim.

The acrosome contains digestive enzymes to enable the sperm to penetrate the surface of the egg.

45
Q

How are palisade mesophyll cells specialised for their functions?

A

Are in leaves and do most of the photosynthesis.

They contain many chloroplasts, so they can absorb a lot of sunlight.

The walls are thin, so CO2 can easily diffuse into the cell.

46
Q

How are root hair cells specialised for their functions?

A

They absorb water and mineral ions from the soil.

They have a large surface area for absorption and a thin, permeable cell wall, for entry of water and ions.

The cytoplasm contains extra mitochondria to provide the energy the energy needed for active transport.

47
Q

How are guard cells specialised for their functions?

A

They are found in pairs, with a gap between them to form a stoma/stomata- pore is used for gas exchange of leaf.

In the light, the guard cells take up water into the vacuoles and become turgid. Their thin outer walls and thickened inner walls force them to bend outwards, opening the stomata- allows for gas exchange in photosynthesis,

48
Q

What are the levels of organisations?

A

The cell is the ‘basic building block of life’ and is the smallest functioning part of an organism.

A group of cells working together is called a tissue and a collection of tissues all performing a specific function is called an organ.

Multiple organs which are connected together are referred to as an organ system.

49
Q

What is a squamous epithelium tissue?

A

It is a single layer of flat cells lining a surface.

Found in many places int he body -alveoli.

provides a thin exchange surface for substances to diffuse across

50
Q

What is ciliated epithelium?

A

It is a layer of cells covered in cilia.

Found on surfaces where things need to be moved- found in airways where mucus is moved along by the cilia.

51
Q

What is muscle tissue?

A

Is made up of bundles of elongated cells called muscle fibres.

Three different types- Smooth muscle, cardiac muscle and skeletal muscle.

52
Q

What is cartilage?

A

It is a type of connective tissue found in the joint.

It shapes and supports the ears, nose and windpipe.

It is formed when cells called chondroblasts secrete an extracellular matrix ( a jelly-like substance containing protein fibres) which they become trapped inside.

53
Q

What is xylem tissue?

A

It is a plant tissue with 2 jobs- It transports water around the plant and supports the plant.

Contains hollow xylem vessel cells (dead) and living parenchyma cells.

54
Q

What is phloem tissue?

A

It transports sugars around the plant.

It is arranged in tubes and is made up of sieve cells, companion cells, and some ordinary plant cells.

Each sieve cell has end walls (called sieve plates) with holes in them, so that sap can move easily through them.

55
Q

Describe the structure and function of the lungs.

A

It is an animal organ which carries out gas exchange.

They contain squamous epithelium tissue (in alveoli) and ciliated epithelium tissue (in bronchi).

They have elastic connective tissue and vascular tissue (in blood vessels)

56
Q

Describe the structure and function of the leaf.

A

It is a plant organ that also carries out gas exchange and photosynthesis.

Contains palisade tissue, epidermal tissue (to prevent water loss from the leaf). and xylem and phloem tissues in the veins.

57
Q

What is the respiratory system made up of?

A

Lungs
Trachea
Larynx
Nose
Mouth
Diaphragm

58
Q

What is the circulatory system made up of?

A

Heart
Artery
Veins
Capillaries

Biology: Paper 1 (24 decks)

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