Cells 2.1-2.2

Question 1

Structure of eukaryotic cells

Answer 1

Cell surface membrane 
Nucleus 
Mitochondria
Chloroplasts
Golgi Apparatus and Golgi vesicles 
Lysosomes 
Ribosomes
Rough and smooth endoplasmic reticulum 
Cell wall
Cell vacuole

Question 2

The nucleus structure

Answer 2

Nuclear envelope
Nuclear pores
Nucleoplasm
Chromosomes
Nucleolus

Question 3

Nucleus’ functions

Answer 3

Act as the control centre of the cells through the production of mRNA and tRNA and hence protein synthesis
Retain the genetic material of the cell in the form of DNA and chromosomes
Manufacture ribosomal RNA and ribosomes

Question 4

Nuclear envelope

Answer 4

A double membrane that surrounds the nucleus. It’s outer membrane is continuous with the endoplasmic reticulum of the cell and often has ribosomes on the surface. It controls the entry and exit of materials in and out of the nucleus and contains the reactions taking place within it

Question 5

Nuclear pores

Answer 5

Allow the passage of large molecules, such as messenger RNA, out of the nucleus. There are typically around 3000 pores in each nucleus

Question 6

Nucleoplasm

Answer 6

The granular, jellylike material that makes up the bulk of the nucleus

Question 7

Chromosomes

Answer 7

Consist of protein-bound, linear DNA

Question 8

Nucleolus

Answer 8

A small spherical region within the nucleoplasm. It manufactures ribosomal RNA and assembles the ribosomes. There may be more than one nucleolus in the nucleus

Question 9

mitochondria’s structure

Answer 9

Double membrane
Cristae
Matrix

Question 10

Mitochondria’s double membrane

Answer 10

Around the organelle is a double membrane that controls the entry and exit of material. The inner of the two membranes is folded to form extensions known as Cristae

Question 11

Cristae

Answer 11

Are extensions of the inner membrane, which in some species extend across the whole width of the mitochondrion. These provide a large surface area for the attachment of enzymes and other proteins involved in respiration

Question 12

Matrix

Answer 12

The matrix makes up the remainder of the mitochondrion. It contains protein, lipids, ribosomes and DNA that allows the mitochondria to control the production of some of their own proteins. Many enzymes involved in respiration are found in the matrix

Question 13

Mitochondria’s function

Answer 13

Mitochondria are the sites of the aerobic stages of respiration
They are therefore responsible for the production of the energy carrier molecule, ATP, from respiratory substrates such as glucose. Because of this, the number and size of mitochondria, and the number of the Cristae, are high in cells that have a high level of metabolic activity and therefore require a plentiful supply of ATP. Examples of metabolically active cells include muscle and epithelial cells.

Question 14

Chloroplasts structure

Answer 14

The chloroplast envelope
The grana
Thylakoids
Chlorophyll
The stroma

Question 15

The chloroplast Envelope

Answer 15

A double plasma membrane that surrounds the organelle

It is highly selective in what it allows to enter and leave the chloroplast

Question 16

The grana

Answer 16

Are stacks of up to 100 disc like structures called thylakoids
Within the thylakoids is the photosynthetic pigment called chlorophyll
Some thylakoids have tubular extensions that join up with thylakoids in adjacent grana
Grana are where the first stage of photosynthesis (light absorption) takes place

Question 17

The stroma

Answer 17

A fluid filled matrix where the second stage of photosynthesis (synthesis of sugars) takes place
Within the stroma are a number of other structures, such as grains

Question 18

Chloroplast adaptions for function of harvesting sunlight and carrying out photosynthesis

Answer 18

the granal membranes provide a large surface area for the attachment of chlorophyll, electron carriers and enzymes that carry out the first stage of photosynthesis. These chemicals attach the membrane in a highly ordered fashion
The fluid of the stroma possesses all the enzymes needed to make sugars in the second stage of photosynthesis
Chloroplasts contain both DNA and ribosomes so they can quickly and easily manufacture some of the proteins needed for photosynthesis

Question 19

Rough endoplasmic reticulum

Answer 19

Has ribosomes present on the outer surfaces of the membranes.

Question 20

Endoplasmic reticulum

Answer 20

An elaborate, three-dimensional system of sheet-like membranes, spreading through the cytoplasm of the cells
It is continuous with the outer nuclear membrane. The membranes enclose a network of tubules and flattened sacs called cisternae. There are two types of ER

Question 21

Smooth endoplasmic reticulum

Answer 21

Lacks ribosomes on its surface and is often more tubular in appearance

Question 22

RER functions

Answer 22

Provide a large surface area for the synthesis of proteins and glycoproteins
Provide a new pathway for the transport of materials, especially proteins, throughout the cell

Question 23

SER functions

Answer 23

Synthesise, store and transport lipids

Synthesise, store and transport carbohydrates

Question 24

Golgi apparatus function

Answer 24

Add carbohydrate to proteins to form glycoproteins
Produce Secretary enzymes, such as those secreted by the pancreas
Secrete carbohydrates, such as those used in making cells walls in plants
Transport, modify and store lipids
Form lysosomes

Question 25

Golgi apparatus sequence

Answer 25

The proteins and lipids produced by the ER are passed through the Golgi apparatus in strict sequence. The Golgi modifies proteins often adding nonprotein components such as carbohydrates to them It also ‘labels’ them, allowing them to be accurately sorted and sent to the correct destinations Once sorted, modified proteins and lipids are transported in Golgi vesicles

Question 26

Lysosomes functions

Answer 26

Hydrolyse material ingested by phagocytic cells, such as white blood cells and bacteria Release enzymes to the outside of the cell in order to destroy material around the cell Digest worn out organelles so that the useful chemicals they are made of can be reused Completely break down cells after they have died

Question 27

How are lysosomes formed

Answer 27

Formed when the vesicles produced by the Golgi apparatus contain enzymes such as proteases and lipases Lysosomes are a type of Golgi vesicle that releases lysozymes

Question 28

Ribosomes structure

Answer 28

Small cytoplasmic granules found in all cells They may occur in the cytoplasm or be associated with the RER Have two subunits – one large and one small – each of which contains ribosomal RNA and protein

Question 29

Two types of ribosomes

Answer 29

80S – found in eukaryotic cells, is around 25 nm in diameter | 70 S – found in prokaryotic cells, mitochondria and chloroplasts, is slightly smaller

Question 30

Ribosomes function

Answer 30

Despite the small size, they are quite in such fast numbers that they can account for up to 25% of the dry mass of the cell The site protein synthesis

Question 31

Cell wall features

Answer 31

Consist of a number of polysaccharides, such as Celulose There is a thin layer called the middle lamella, which marks the boundary between adjacent cells and cements adjacent cells together

Question 32

Cell wall functions

Answer 32

Provide mechanical strength in order to prevent the cell busting under the pressure created by the osmotic entry of water To give mechanical strength to the plant as a whole To allow water to pass along it and so contribute to the movement of water through the plants

Question 33

Vacuoles functions

Answer 33

Support herbaceous plants, and herbaceous parts of woody plants, making cells turgid Sugars and amino acids may act as a temporary food store The pigments may colour petals to attract pollinating insects

Question 34

Vacuoles structure

Answer 34

Fluid filled sac bounded by a single membrane Within mature plant cells there is usually one large central vacuole The single membrane around it is called the tonoplast A plant vacuole contains a solution of mineral salts, sugars, amino acids, wastes and sometimes pigments

Question 35

specialised cells

Answer 35

In complex multi cellular organisms, eukaryotic cells become specialised for specific functions Specialised cells are organised into tissues, tissues into organs and organs into systems

Question 36

Tissues

Answer 36

A collection of similar cells that perform a specific function are known as a tissue Examples of tissues include Epithelials tissues Xylem

Question 37

Epithelial tissues

Answer 37

Found in animals and consist of sheets of cells They line the surface of organs and often have a protective or secretary function There are many similar types, including those made up of thin, flat cells that line organs where diffusion takes place, for example the alveoli of the lungs, and ciliated epithelium that lines a duct such as the trachea The cilia are used to move the mucus over the epithelial surface

Question 38

Xylem

Answer 38

Occurs in plants and is made up of a number of similar cell types It is used to transport water and mineral ions throughout the plant and also gives mechanical support

Question 39

Organs

Answer 39

An organ is a combination of tissues that are coordinated to perform a variety of functions, although they often have one predominant major function In animals for example, the stomach is an organ that is involved in the digestions of certain types of food It is made up of tissues such as: Muscles to churn and mix the stomach contents Epithelium to protect the stomach wall and produce secretions Connective tissue to hold together the other tissues

Question 40

Organ systems

Answer 40

Organs work together as a single unit known as an organ system The systems may be grouped together to perform particular functions more efficiently There are number of organ systems in humans The digestive system The Respiratory system The circulatory system

Question 41

How do prokaryotic cells differ from eukaryotic cells

Answer 41

Prokaryotic cells are much smaller Have cytoplasm that lacks membrane-bound organelles Have smaller ribosomes Have no nucleus; instead they have a singular DNA molecule that is free in the cytoplasm and is not associated with proteins Have a cell wall that contains murein, a glycoprotein They have one or more plasmids whereas eukaryotic cells have none They have a capsule surrounding the cell They have one or more flagella

Question 42

Capsule role (prokaryotic cell)

Answer 42

Protects bacteria from other cells and helps groups of bacteria to stick together for further protection

Question 43

Circular DNA role (prokaryotic cells)

Answer 43

Possesses the genetic information for the replication of bacterial cells

Question 44

Plasmid role (prokaryotic cells)

Answer 44

Possesses the genes that may aid the survival of bacteria in adverse conditions, e.g. produces enzymes that break down antibiotics

Question 45

Viruses

Answer 45

They are acellular, nonliving particles They are smaller than bacteria They contain nucleic acids such as DNA or RNA as genetic material but can only multiply inside living host cells The Nucleic acid is enclosed within a protein coat called the capsid Some viruses, like the human in immunodeficiency virus, are further surrounded by a lipid envelope. The Lipid envelope, or if this is not present, the Capsid, have attachment proteins which are essential to allow the virus to identify and attach to a host cell

Question 46

2 types of microscope

Answer 46

Light and Electron (transmission and scanning)

Question 47

Which microscope has highest magnification

Answer 47

TEM > SEM > LM x12,000,000 x200,000 x2,000

Question 48

Which microscope has higher resolution

Answer 48

TEM > SEM > LM 0.1nm 20nm 200nm

Question 49

Resolution

Answer 49

minimum distance at which 2 very close objects can be distinguished

Question 50

1mm=?um

Answer 50

1000um

Question 51

1mm=?nm

Answer 51

1,000,000 nm

Question 52

Magnification formula

Answer 52

magnification = image size/actual size

Question 53

Why does electron microscopes have a higher resolution?

Answer 53

Electron microscope uses electrons ​which have a shorter wavelength (light microscope uses light which has a large wavelength)

Question 54

Difference between TEM and SEM?

Answer 54

in Transmission the electrons pass through the specimen, in Scanning the electrons bounce off the specimen's surface

Question 55

Advantages and disadvantages of TEM

Answer 55

− Advantage = highest magnification and highest resolution − Disadvantage = works in a vacuum so can only observe dead specimens, specimen needs to be thin, black and white image, 2D image, image may contain artefacts, complicated staining process is required and can build up 3D image but is slow and complicated process

Question 56

What are artefacts

Answer 56

Things that result from the way the specimen is prepared Artefacts may appear on the finished photomicrograph but are not part of the natural specimen It is therefore not always easy to be sure that what we see on the photomicrograph really exists in that form

Question 57

Advantages and disadvantages of SEM

Answer 57

− Advantage = produces 3D image, doesn’t need to be thin specimen as electrons don’t penetrate − Disadvantage = works in a vacuum so can only observe dead specimens, black and white image, artefacts, complex staining process,

Question 58

Cell fractionation

Answer 58

Process where cells are broken up and different organelles they contain are separated out

Question 59

Cell fractionation process

Answer 59

Tissues placed in cold, buffer solution of the same water potential as the tissue: Homogenation: cells are broken up by homogeniser (blender). Releases organelles from cell. Resultant fluid (homogenate) is then filtered to remove any complete cells and large pieces of debris Ultracentrifugation: where fragments are separated in a centrifuge whuc spins filtrate at high speed in the following way; tube of filtrate spun at low speed which forces the heaviest organelles (nuclei) to the bottom where they form a pellet or sentiment; fluid (supernatant) at the top is removed and placed in another tube which is spun at a faster speed which removes the next heaviest organelle (mitochondria). this process is repeated for each of the organelles

Question 60

Cell fractionation required conditions

Answer 60

– COLD buffer solution – prevents enzyme activity that might break down organelle – same water potential – prevent organelles from bursting/shrinking – buffered – pH doesn’t fluctuate (alters structure

Question 61

Scientific community and artefacts

Answer 61

There was a considerable period of time during which the scientific community distinguished between artefacts and cell organelles

Question 62

By what processes can cell division take place

Answer 62

Mitosis or meiosis

Question 63

Mitosis versus meiosis

Answer 63

Mitosis – produces two daughter cells that have the same number of chromosomes as the parent cell and each other Meiosis – produces four daughter cells, each with half the number of chromosomes as the parent cell

Question 64

Mitosis

Answer 64

Division of a cell results in each of the daughter cells having an exact copy of the DNA of the parent cell Except in the rare event of the mutation, the genetic make up of two daughter nuclei is also identical to that of the parent nucleus Mitosis is always preceded by the period during which the cell is not dividing. This period is called interphase. Its is a period of considerable cellular activity that includes a very important event, the replication of DNA The two copies of DNA after replication remain joined at a place called the centromere. Although mitosis is a continuous process it can be divided into four stages convenience: Prophase, metaphase, anaphase and telophase

Question 65

Three stages of interphase

Answer 65

G1– first growth phase- longest phase S – replication phase G 2 –second growth phase – short

Question 66

G1-first growth phase

Answer 66

Protein synthesis – cell grows Most organelles produced Volume of cytoplasm increases Cell differentiation (switching on or off of genes) Length depends on internal and external factors If cell is not going to divide again it remains in this phase DNA content = 20

Question 67

S – replication phase

Answer 67

DNA replication – this must occur if mitosis is to take place The cell enters this phase only if cell division is to follow DNA content = 40

Question 68

G2 – second growth phase

Answer 68

Short gap before mitosis (cell division) Cytoskeleton of cell breaks down and the protein microtubule components begin to reassemble into spindle fibres – required for cell division DNA content = 40

Question 69

4 mitotic phases

Answer 69

``` Prophase Metaphase Anaphase Telophase (I) punched my annoying teacher ```

Question 70

Eukaryotic cells that do retain the ability to divide show:

Answer 70

A cell cycle

Question 71

When does DNA replication occur in the cell cycle

Answer 71

Interphase

Question 72

Prophase

Answer 72

The chromosomes first become visible, initially as long thin fibres, which later shorten and thicken. Animal cells contain two cylindrical organelles called centrioles, each of which moved to opposite ends (called Poles) of the cell From each of the centrioles, spindle fibres develop from pole to pole (collectively called spindle apparatus) The nucleolus disappears and the nuclear envelope breaks down, leaving the chromosomes free in the cytoplasm of the cell These chromosomes are drawn towards the equator of the cell by the spindle fibres attached the centromere

Question 73

Metaphase

Answer 73

The chromosomes are seen to be made up of two chromatids Each chromatid is an identical copy of DNA from the parent cell The chromatids are joined by the centromere It is to this centromere that some microtubules from the poles are attached, and the chromosomes are pulled along by the spindle apparatus and arrange themselves across the equator of the cell

Question 74

Anaphase

Answer 74

The centromeres divide into two and the spindle fibres pull the individual chromatids making up the chromosomes apart The chromatids move rapidly to the respective, opposite poles of the cell and we now refer to them as chromosomes The energy for the process is provided by mitochondria which gather around the spindle fibres If cells are treated with chemicals that destroy the spindle, the chromosomes remain at the equator, unable to reach the polls

Question 75

Telophase

Answer 75

The chromosomes reach their respective poles and become longer and thinner, finally disappearing altogether, leaving only widely spread chromatin Spindle fibres disintegrate and the nuclear envelope and nucleolus reform

Question 76

What happens after mitosis in the cell cycle

Answer 76

Cytokinesis

Question 77

Cytokinesis

Answer 77

Process where the cytoplasm divides Cell divides into two DNA content = 20

Question 78

Mitosis phases and simple description of each phase

Answer 78

Prophase: DNA coils to form chromosomes, nucleus breaksdown, spindle fibres form ​Metaphase: chromosomes line up in middle of cell and attach to spindle fibre via centromere ​Anaphase: spindle fibres pull, centromere splits, sister chromatids move to opposite sides ​Telophase: chromatids uncoil, nucleus reforms (left with 2 genetically identical nuclei)

Question 79

Difference between chromatin, chromosomes and chromatids

Answer 79

- Chromatin is composed of DNA and histones that are packaged into thin, stringy fibers. These chromatin fibers are not condensed. During cell division, chromatin condenses to form chromosomes. - Chromosomes are single-stranded groupings of condensed chromatin. During the cell division processes of mitosis and meiosis, chromosomes replicate to ensure that each new daughter cell receives the correct number of chromosomes. A duplicated chromosome is double-stranded and has the X shape. The two strands are identical and connected in a central region called the centromere. - A chromatid is either of the two strands of a replicated chromosome. Chromatids connected by a centromere are called sister chromatids. At the end of cell division, sister chromatids separate, becoming daughter chromosomes in the newly formed daughter cells.

Question 80

Explain the appearance of cells in interphase stage of cell cycle

Answer 80

One cell | Genetic material not in chromosomes, in chromatin inside nucleus, all bundled in circular form

Question 81

Explain the appearance of cells in prophase stage of mitosis

Answer 81

One cell | Chromosomes are bundled together in the centre circular form (in nucleus)

Question 82

Explain the appearance of cells in metaphase stage of mitosis

Answer 82

One large cell | Chromosomes all lined up in centre of cell

Question 83

Explain the appearance of cells in anaphase stage of mitosis

Answer 83

One cell | DNA in chromosomes at separate poles of cell

Question 84

Explain the appearance of cells in telophase stage of mitosis

Answer 84

One cell Chromatin in two separate bundles at opposite sides of cell Doesn’t look like chromosomes – widely spread in circular shapes

Question 85

Uncontrolled cell division

Answer 85

Mitosis is a controlled process Uncontrolled cell division can lead to the formation of tumours and of cancers Many cancer treatments are directed at controlling the rate of cell division

Question 86

Cell division in prokaryotic cells

Answer 86

Binary fission

Question 87

Binary fission process

Answer 87

– The circular DNA molecule replicates and both copies attach to the cell membrane – the plasmids also replicate – the cell membrane begins to grow between the two DNA molecules and begins to pinch inwards, dividing the cytoplasm in two – a new cell wall formed between the two molecules of DNA, dividing the original cell into two identical daughter cells, each with a single copy of the circular DNA and variable number of copies of the plasmids

Question 88

Why don’t viruses undergo cell division?

Answer 88

They are nonliving

Question 89

Replication of viruses

Answer 89

They replicate by attaching to the host cell with the attachment proteins on the surface They then inject their nucleic acid into the host cell The genetic information on the injected viral nucleic acid then provides the instructions for the host cell’s metabolic processes to start producing the viral components, nucleic acid, enzymes and structural proteins, which are then assembled into new viruses

Question 90

What is mitosis needed for

Answer 90

Growth Repair Reproduction (asexual)

Question 91

Cells that don’t divide continually

Answer 91

Still undergo a regular cycle of division separated by periods of cell growth This is known as the cell cycle and has three stages: Interphase – which occupies most of the cell cycle, and is sometimes known as the resting phase because no division takes place Nuclear division – when the nucleus divides either in two (mitosis) or four (meiosis) Division of the cytoplasm – the process by which the cytoplasm divides to produce two new cells or four new cells

Question 92

Cancer

Answer 92

cancer cells are rapidly dividing cells (like hair cells, skin cells, red blood cells), they spend less time in interphase and more time in the other stages (mitosis)

Question 93

Treatments for cancer

Answer 93

Surgery = aim is to remove tumour ​Chemotherapy = - using drugs that inhibit mitosis in rapidly dividing cancer cells ​ - problem, also affect normal healthy cells (hair cell, skin cells, rbcs) ​ ​ causing side effects (hair loss, dry skin, tiredness) ​ - treatment given as regular doses to allow time for normal healthy ​ ​ cells to recover in number ​Radiotherapy = radiation used to destroy cancer cells