Cell division and Cellular Organisation

Question 1

What is the Cell cycle?

Answer 1

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

Question 2

When does the cell cycle start and end?

Answer 2

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

Question 3

What is interphase?

Answer 3

It is the period of cell growth and DNA replication.

Question 4

What is the M phase?

Answer 4

It is a period of cell division that involves mitosis (nuclear division) and Cytokinesis (Cytoplasmic division)

Question 5

What sub-phases is interphase divided into?

Answer 5

G1, S and G2

Question 6

Why are checkpoints needed in the cell cycle?

Answer 6

They occur at key points during the cycle to make sure it’s ok for the process to continue as any abnormalities would cause severe problems/Replication needs to be exact to conserve DNA.

Question 7

What happens at G1 (Growth Phase 1)?

Answer 7

The cell grows and new organelles and proteins are made

Question 8

What happens at G1 checkpoint?

Answer 8

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

Question 9

What happens at S (Synthesis) Phase?

Answer 9

The cell replicates its DNA, ready to divide by mitosis

Question 10

What happens at G2 (Growth Phase 2)?

Answer 10

The cell keeps growing and proteins needed for cell division are made

Question 11

What happens at G2 Checkpoint?

Answer 11

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

Question 12

Why is mitosis needed?

Answer 12

It is needed for the growth of multicellular organisms and for repairing damaged tissues. It is also a method of asexual reproduction for some plants, animals, and fungi.

Question 13

What are the phases of Mitosis?

Answer 13

Prophase
Metaphase
Anaphase
Telophase

Question 14

What occurs during Interphase?

Answer 14

The cell carries out normal functions but also prepares to divide. The cell’s DNA is unraveled and replicated, to double its genetic content. The Organelles are also replicated so it has spare ones, and it’s ATP content is increased (provides energy for cell division)

Question 15

What occurs during Prophase?

Answer 15

• The chromosomes condense, getting shorter and fatter
• Tiny bundles of protein called centrioles start to move to opposite ends/poles of the cell forming a network of fibers called spindle fibers.
• The nuclear envelope breaks down and chromosomes lie free in the cytoplasm

Question 16

What is the centromere?

Answer 16

The point where two sister chromatids are joined to form one chromatid/chromosome

Question 17

What occurs during Metaphase?

Answer 17

• The chromosomes line up along the middle of the cell
• They become attached to spindle fibers via their centromere
• At the metaphase checkpoint the cell checks that all the chromosomes are attached to the spindle fibres before mitosis can continue

Question 18

What occurs during Anaphase?

Answer 18

• The centromeres divide, separating each pair of sister chromatids. The spindles contract, pulling chromatids to opposite ends of the cell, centromere first.

Question 19

What occurs during Telophase?

Answer 19

• The chromatids reach the opposite poles on the spindle.
• They uncoil and become long and thin again.
• They are now chromosomes again
• The nuclear envelope is reformed around each group of chromosomes, so there are now two nuclei

Question 20

What occurs during Cytokinesis?

Answer 20

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 each other. Cytokinesis usually begins in anaphase and ends in telophase. It’s a separate process from mitosis.

Question 21

How can you observe the cell cycle and mitosis?

Answer 21

You can actually observe it using a light microscope at different stages by using a stain to stain the chromosomes.

Question 22

What occurs in sexual reproduction?

Answer 22

Two gametes join together at fertilisation to form a zygote which then divides and develops into a new organism.

Question 23

What is meiosis?

Answer 23

Meiosis is a type of cell division that happens in the reproductive organs to produce gametes. It involves a reduction division. Cells that divide by meiosis have the full number of chromosomes to start with by the cells that are formed have half (Haploid cells). Cells formed are all genetically different as each new cell ends up with a different combination of chromosomes.

Question 24

What are the stages of meiosis?

Answer 24

It involves two divisions: Meiosis I and Meiosis II. Meiosis I is the reduction division. (each one has its own Prophase, Metaphase, etc.)

Question 25

What occurs during Meiosis I?

Answer 25

Prophase: chromosomes condense and arrange themselves in homologous pairs, and crossing over occurs, centrioles use spindle fibers, nuclear envelope breaks down
Metaphase: Homoglous pairs line up along the center and attach to spindle fibers
Anaphase: The spindles contract, separating the homologous pairs.
Telophase: A nuclear envelope forms around each group of chromosomes
Cytokinesis: Division of cytoplasm occurs and two haploid daughter cells are produced.

Question 26

What occurs during Meiosis II?

Answer 26

The same processes in meiosis I occur except in anaphase II, where the pairs of sister chromatids are separated- each new daughter cell inherits one chromatid from each chromosome. Four genetically different haploid daughter cells are produced- these are the gametes

Question 27

What is ‘Crossing over’ in prophase I in Meiosis?

Answer 27

The homologous pairs of chromosomes come together and pair up. The chromatids twist around each other and bits of chromatids swap over. The chromatids still contain the same genes but now have a different combination of alleles.

Question 28

How does the crossing over of chromatids in Meiosis cause genetic variation?

Answer 28

The crossing over of chromatids in meiosis I means that each of the four daughter cells formed from meiosis contains chromatids with different alleles.

Question 29

How does the independent assortment of chromosomes lead to genetic variation in Meiosis?

Answer 29

• each homologous pair is made up of one from your mum and one from your dad
• when they line up it is random which chromosome from each pair ends up in each cell
• so the four daughter cells have different combinations of the maternal and paternal chromosomes.
• this is called independent assortment separation of the chromosomes

Question 30

What are stem cells?

Answer 30

They are unspecialized cells that can develop into different types of cells, like liver cells, white blood cells, and other specialized cells. All multicellular organisms have some form of stem cell. They can also divide to create more stem cells (self renewing)

Question 31

Where are stem cells found in humans?

Answer 31

They are found in early embryos and a few places in adults. Stem cells in early embryos can develop into any type of human cell. Stem cells in adults can only develop into a limited range of cells.

Question 32

What is cell differentiation?

Answer 32

It is the process stem cells undergo to become specialized and perform a specific function

Question 33

Why do animals use stem cells?

Answer 33

Adult stem cells are used to replace damaged cells, e.g. to make new skin or blood cells.

Question 34

Why do plants use stem cells?

Answer 34

Plants are always growing, so stem cells are needed to make new shoots and roots throughout their lives. Stem cells in plants can differentiate into various plant tissues including the xylem and phloem.

Question 35

What do cells in bone marrow differentiate into?

Answer 35

• Bones are living organs, containing nerves and blood vessels
• The main bones of the body have marrow in the center
• Here adult stem cells divide and differentiate to replace worn-out blood cells. (erythrocytes or neutrophils)

Question 36

What do cells in meristems differentiate into?

Answer 36

• in plants stem cells are found in the meristems (meristematic tissue)
• in the root and stem, stem cells of the vascular cambium divide and differentiate to become xylem vessels and phloem sieve tubes

Question 37

Why do people think stem cells could help cure diseases like Parkinson’s?

Answer 37

They think they can be used to replace damaged tissues in a range of diseases.
alzheimers= nerve cells in the brain
parkinsons= specific nerve cells in the brain

Question 38

How are Neutrophils specialized for their function?

Answer 38

They are a type of white blood cell that defends the body against disease. They are flexible to allow them to engulf foreign particles or pathogens. They have many lysosomes in their cytoplasm which contains digestive enzymes to break down the engulfed particles.

Question 39

How are Erythorocytes specialized for their function?

Answer 39

They are red blood cells and they carry oxygen in the blood. The biconcave disk shape provides a large surface area for gas exchange. They have no nucleus so there is more room for haemoglobin.

Question 40

How are Epithelial specialized for their function?

Answer 40

They are cells that cover the surfaces of organs. The cells are joined by interlinking cell membranes and a membrane at their base. Ciliated epithelial cells have cilia that beat to move particles away. Squamous epithelia are very thin to allow diffusion of gases efficiently.

Question 41

How are Sperm cells specialized for their function?

Answer 41

Sperm cells have a flagellum so they can swim to the egg. They also have lots of mitochondria to provide the energy to swim. The acrosome contains digestive enzymes to enable the sperm to penetrate the surface of the egg.

Question 42

How are Palisade mesophyll cells specialized for their function?

Answer 42

They are found in leaves and they do most of the photosynthesis. They contain many chloroplasts, so they can absorb a lot of sunlight. The walls are thin so carbon dioxide can easily diffuse into the cell.

Question 43

How are Root hair cells specialized for their function?

Answer 43

They absorb water and mineral ions from the soil. They have a large surface area for absorption and a thin, permeable cell wall, for the entry of water and ions. The cytoplasm contains extra mitochondria to provide the energy needed for active transport.

Question 44

How are Guard cells specialized for their function?

Answer 44

They are found in pairs, with a gap between them to form a stoma. This is one of the tiny pores in the surface of the leaf used for gas exchange. In the light, guard cells take up water and become turgid. Their thin outer walls and thickened inner walls force them to bend outwards, opening the stomata. This allows the leaf to exchange gases for photosynthesis.

Question 45

What is a tissue?

Answer 45

A tissue is a group of cells that are specialized to work together to carry out a particular function. A tissue can contain more than one cell type.

Question 46

What is Squamous epithelium?

Answer 46

It is a single layer of flat cells lining a surface. It’s found in many places, including the alveoli in the lungs.

Question 47

What is Ciliated epithelium?

Answer 47

It is a layer of cells covered in cilia. It is found on surfaces where things need to be moved. For example: the trachea, where cilia waft mucus along.

Question 48

What is muscle tissue?

Answer 48

It is made up of bundles of elongated fibers. There are three different types of muscle tissue:
- smooth (in the stomach wall)
- cardiac (in the heart)
- skeletal (used to move)

Question 49

What is cartilage?

Answer 49

It is a type of connective tissue found in the joints. It also shapes and supports the ears, nose, and windpipe. It’s formed when cells called chondroblasts secrete an extracellular matrix (a jelly-like substance containing protein fibers) which they become trapped inside.

Question 50

What is Xylem tissue?

Answer 50

It is a plant tissue with two jobs:
- transports water around the plant
- it supports the plant
it contains hollow xylem vessel cells, which are dead and living parenchyma cells.

Question 51

What is Phloem tissue?

Answer 51

It transports sugars around the plant. It’s arranged in tubes and is made up of sieve cells, companion cells, and some ordinary plant cells. Each sieve cell has end walls with holes in them, so that sap can move easily through them. These end walls are called sieve plates.

Question 52

What is an organ?

Answer 52

An organ is a group of different tissues that work together to perform a particular function.

Question 53

What tissues do the lungs contain?

Answer 53

They contain Squamous epithelial tissue (in alveoli) and ciliated epithelial tissue (in bronchi) and they also have elastic tissue and vascular tissue (in the blood vessels)

Question 54

What tissues do leaves contain?

Answer 54

They contain palisade tissue for photosynthesis, as well as epidermal tissue (to prevent water loss from the leaf), and xylem and phloem tissues in the veins.

Question 55

What is an organ system?

Answer 55

Organs work together to form organ systems and each system has a particular function

Question 56

What organs make up the respiratory system?

Answer 56

It is made up of all the organs, tissues, and cells involved in breathing. The lungs, trachea, larynx, nose, mouth, and diaphragm are all part of the respiritory system.

Question 57

What organs make up the circulatory system?

Answer 57

The circulatory system is made up of the organs, involved in the blood supply. The heart, arteries, veins, and capillaries are all parts of this system.