Cell Structure

Question 1

Cell

Answer 1

Basic unit of all living organisms; it is surrounded by a cell surface membrane and contains genetic material (DNA) and cytoplasm containing organelles

Question 2

Orgenelle

Answer 2

A functionally and structurally distinct part of a cell, e.g. a ribosome or mitochondrion

Question 3

Nucleus

Answer 3

Large organelle found in eukaryotic cells, but absent from prokaryotic cells; the nucleus contains the cell’s DNA and therefore controls the activities of the cell; it is surrounded by two membranes which together form the nuclear envelope

Question 4

Eukaryotes

Answer 4

Organisms made of cells with membrane-bound nuclei and are taught to be evolved from prokaryotes.

Question 5

Prokaryotes

Answer 5

an organism whose cells do not contain a nucleus or any other membrane-bound organelles

Question 6

Cell Surface membrane

Answer 6

Very thin membrane (about 7 nm diameter) surrounding all cells; it is partially permeable and controls the exchange of materials between the cell and its environment

Question 7

Chromatin

Answer 7

The material which chromosomes are made of, it contains DNA, proteins and small amounts of RNA. Visible as patches in the nucleus.

Question 8

Chromosome

Answer 8

A structure made of tightly coiled chromatin, present in the nucleus of eukaryotic cells. Visible during cell division; the term ‘circular DNA’ is now also commonly used for the circular strand of DNA present in a prokaryotic cell

Question 9

Nucleolus

Answer 9

A small structure, one or more of which is found inside the nucleus; the nucleolus is usually visible as a densely stained body; its function is to manufacture ribosomes using the information in its own DNA

Question 10

Protoplasm

Answer 10

All living materials inside the cell (cytoplasm+nucleus)

Question 11

Mitochondria

Answer 11

the organelle in eukaryotes in which aerobic respiration takes place

Question 12

Cell wall

Answer 12

A wall surrounding prokaryote, plant and fungal cells; the wall contains a strengthening material which protects the cell from mechanical damage, supports it and prevents it from bursting by osmosis if the cell is surrounded by a solution with a higher water potential

Question 13

Centriole

Answer 13

Small structures close to the nucleus.

Question 14

Cell walls and plasmodesmata

Question 15

Microvilli

Answer 15

small, finger-like extensions of a cell which increase the surface area of the cell for more efficient absorption
or secretion

Question 16

Nucleus

Answer 16

• Nuclear envelope
• Chromosomes and Chromatins
• Nucleolus

Question 17

Nuclear Envelope

Answer 17

The nucleus is surrounded by 2 membranes which make the nuclear envelope. the outer membrane is continuous as the endoplasmic reticulum.

The pores present all around the nuclear envelope allows exchange of substances (RNA, ribosomes) and (Nucleotides, ATP) between the nucleus and the cytoplasm

Question 18

Chromosomes and Chromatin

Answer 18

Nucleus contains chromosomes which contains DNA, DNA is fictional units known as genes. They control the cell and inheritance.

Long DNA strands are folded by combining with proteins known as histones to prevent tangling. The combination of DNA and proteins is known as chromatin

Question 19

Nucleolus

Answer 19

Makes ribosomes using the information contained within its own DNA. It contains chromosomes which store genes for different ribosomes. the more ribosomes it makes the larger the nucleolus.

The different parts of the nucleolus comes together only during manufacturing and separate when, as during nuclear division, ribosome synthesis ceases. It then disappears.

Question 20

Endoplasmic Reticulum

Answer 20

The membranes of ER forms flattened compartments called cisternae. Process take place in the cisternae seperated from the cytoplasm.

Question 21

Rough Endoplasmic Reticulum

Answer 21

Covered in many tiny organelles called ribosomes.

Question 22

Smooth Endoplasmic Reticulum

Answer 22

It lacks ribosomes thus smooth, Its function is to produce lipids and steroids such as cholesterol, oestrogen and testosterone. SER is also a major storage site for calcium ions.

Question 23

Ribosomes

Answer 23

Measured in S units (Svedberg units), to determine the speed the ribosomes sediments. Eukaryotic cells usually contain 80S and prokaryotic cells contain 70S ribosomes. Ribosomes are made from combination of RNA and protein.

Question 24

Golgi apparatus

Answer 24

Stack of flattened discs named cisternae. More than one golgi apparatus is present in every cell. The stack is constantly being formed at one end from vesicles which bud off from the ER, and are broken down again at the other end to form Golgi vesicles.

The golgi apparatus collects and processes molecules, especially from the RER, using its 100’s of enzymes. Then the molecules is transported to other parts of the cell or out of the cell through secretion down the secretory pathway.

Question 25

Lysosome

Answer 25

a spherical organelle found in eukaryotic cells; it contains digestive (hydrolytic) enzymes and has a variety of destructive functions, such as removal of old cell organelles.
Simple sacs surrounded by a single membrane, usually 0.1 to 0.5 um in dia.

Contains ezymes called hydrolases as they carry out hydrolysis reactions. However lysosomes must be seperated from other components. Contents in lysosomes are acidic as hydrolysis work best in acid.

Enzymes (proteases, lipases and nucleases) are provided by the golgi apparatus.

Question 26

Getting rid of unwanted cell components

Answer 26

Lysosomes engulf and destroy unwanted cell components

Question 27

Self-digestion

Answer 27

The contents of lysosome is released into the cell which causes the entire cell to digest by a process known as autolysis. Examples (tadpole tails) and (uterus restored to its normal size).

Question 28

Mitochondria

Answer 28

Usually about 1 um in dia, and it usually sausage shaped. They are surrounded by 2 membranes, where the inner membrane is folded to form finger like cristae, which projects inside the mitochondria, to form the matrix. The space between the two membranes is known as the inter membrane space. They are present numerously in cells that require large amounts of energy.

The reactions of respiration takes place inside the solution present in the matrix

Question 29

ATP

Answer 29

Adenine triphosphate

Question 30

Microtubules

Answer 30

Long, rigid, around 25nm in dia. They make up the cytoskeleton along with actin filaments and intermediate filaments, which help determine the cell shape.

Made of proteins known as tubulin, which has 2 forms alpha and beta tubulin. These two tubulins combine to make dimers (double molecules) which are then joined ened to end to form pro filaments, through polymerisation.

13 profilaments line end to end in a ring shape to form a microtubule.

Question 31

Functions of Microtubules

Answer 31

During nuclear division, a spindle made of microtubules is used for the separation of chromatids or chromosomes.

Microtubules form part of the structure of centrioles.

Microtubules form an essential part of the mechanism involved in the beating movements of cilia and flagella.

Question 32

Centrioles and centrosomes

Answer 32

Just outside the nucleus, there are 2 centrioles that right angles each other in a region called the centrosomes. Theses are absent in most plant cells.

Centrioles are 500nm long hollow cylinders, each centriole is made of 9 triplets of microtubules.

Question 33

Cilia

Answer 33

whip-like structures projecting from the surface of many animal cells and the cells of many unicellular organisms; they beat, causing locomotion or the movement of fluid across the cell surface

Question 34

Flagella

Answer 34

whip-like structures projecting from the surface of some animal cells and the cells of many unicellular organisms; they beat, causing locomotion or the movement of fluid across the cell surface; they are identical in structure to cilia, but longer

Question 35

Structure of cilium (cillia)

Answer 35

They have 2 microtubules in the centre and a ring of 9 microtubule doublets around the outside, known as the ‘9+2’ struture.

Each MTD contains a A and B. A contains 13 protofilaments and B is attached to A and only has 10 protofilamenrs. Each A microtubule has arms attached to its outside and inside made of the protein dynein

Question 36

Chloroplasts

Answer 36

Has an elongated shape and a 3-10um dia and 2 membranes forming the chloroplast envelope.

The main function of chloroplasts is to carry out photosynthesis. During the first stage of photosynthesis (the light-dependent stage), light energy is absorbed by photosynthetic pigments, particularly chlorophyll. The pigments are found on the membranes of the chloroplast.

The membrane system consists of fluid-filled sacs called thylakoids, which spread out like sheets in three dimensions. These flat discs pile up forming a structure called the grana

The second stage of photosynthesis (the light- independent stage) uses the energy and reducing power generated during the first stage to convert carbon dioxide into sugars. This takes place in the stroma. The sugars made may be stored in the form of starch grains in the stroma.

They have 70S ribosomes and circular DNA.

Question 37

Cell walls

Answer 37

First walls formed by plants are known as primary walls, which are relatively rigid. The primary wall consists of parallel fibers of the polysaccharide cellulose running through a matrix of other polysaccharides such as pectins and hemicelluloses.

In most cells extra layers of cellulose are added to the first layer of the primary wall, forming a secondary wall. In a given layer the cellulose fibres are parallel, but the fibres of different layers run in different directions forming a cross-ply structure which is stronger as a result

Question 38

Functions of cell walls

Answer 38

Mechanical support and strength (Lignification and Turgid tissues)

Cell walls prevent cells from bursting by osmosis if cells are surrounded by a solution with a higher water potential

The system of interconnected cell walls in a plant is called the apoplast

Living connections through neighbouring cell walls, the plasmodesmata, help form another transport pathway through the plant known as the symplast

The cell walls of the root endodermis are impregnated with suberin, a waterproof substance that forms a barrier to the movement of water, thus helping in the control of water and mineral ion uptake by the plant

Question 39

Vacoules

Answer 39

• Support
  The solution in the vacuole is relatively concentrated. Water therefore enters the vacuole by osmosis, inflating the vacuole and causing a build-up of pressure. A fully inflated cell is described as turgid. Turgid tissues help to support the stems of plants that lack wood
• Lysosomal activities
  Plant vacuoles may contain hydrolyses and act as lysosomes.
• Secondary Metabolites
  Anthocyanins are pigments that are responsible for most of the red, purple, pink and blue colours of flowers and fruits. They attract pollinators and seed dispersers.
  Latex, a milky fluid, can accumulate in vacuoles, for example in rubber trees. The latex of the opium poppy contains alkaloids such as morphine from which opium and heroin are obtained.

Food reserves

Waste products

Growth in size

Question 40

Bacteria

Answer 40

A group of single- celled prokaryotic microorganisms; they have a number of characteristics, such as the ability to form spores, which distinguish them from the other group of prokaryotes known as Archaea

Prokaryotic cells are generally about 1000 times smaller in volume and lack a nucleus that is surrounded by a double membrane.

Question 41

Bacteria (Cell Wall)

Answer 41

Bacterial cell walls contain a strengthening material called peptidoglycan

Question 42

Cytoplasm

Answer 42

The cytoplasm does not contain any double membrane- bound organelles

Question 43

Circular DNA