Chapter 6 - Cell Divisions Flashcards
What are the 3 parts of interphase?
G1, S, G2
What happens in G1?
- Organelles replicate
- Cell grows in size
What happens in S?
- DNA is replicated in the nucleus
What happens in G2?
- Energy stores are increased
- Cell continues to grow in size
What is checked at the G1 checkpoint?
- Cell size
- Nutrients
- Growth factors
- DNA damage
What is checked at the G2 checkpoint?
- Cell size
- DNA replication
- DNA damage
What is G0?
The phase when the cell leaves the cycle (resting state)
What are 3 common reasons why cells enter G0?
- The cell has differentiated
- The cell is damaged
- The cell is old
What are senescent cells?
When old cells stop dividing and undergo changes
What is cytokineses?
Where the cytoplasm divides and two cells are produced
What is the spindle assembly check point?
A checkpoint during mitosis where all chromosomes should be attached to spindles and be alligned
What is the spindle assembly check point also known as?
The metaphase checkpoint
What is mitosis?
Nuclear division
What would the indefinite replication of cells lead to?
- Mutations occur during cell division
- Increased cell replication = increased chance of mutation
- Can lead to harmful mutations e.g. tumours/cancer
Why is DNA length give by number of base pairs?
Because DNA is double stranded
What does mitosis produce?
Two identical daughter cells
How are chromatids produced?
When a chromosome is converted into two identical DNA molecules (chromatids)
What is the centromere?
The centre point of two chromatids joining to form a chromosome
How is chromatin produced?
When chromatids and proteins called histones combine
What are the four stages of mitosis?
Prophase, metaphase, anaphase and telophase
What is the acronym to remember the order of mitosis phases?
P-MAT
What happens to the nucleolus during prophase?
It disappears
What do chromatin fibers do during prophase?
They coil and condense to form chromosomes
What do spindle fibres do during prophase?
They move chromosomes to the centre of the cell
What has happened by the end of prophase?
The nuclear envelope has disappeared
What happens in animal and some plant cells during prophase to do with centrioles?
Two centrioles move to opposite poles of the cell
What happens during metaphase?
The chromosomes are moved by the spindle fibres to form a line across the centre of the cell, and then are held in position
What is the metaphase plate?
The (invisible) line through the centre of the cell, where chromosomes line up (during metaphase)
What happens during anaphase?
The centromeres holding the pairs of chromatids together in each chromosome divide
The chromatids are separated and pulled to opposite poles of the cell by the shortening of the spindle fibres
When does cytokinesis begin?
During telophase
What happens during telophase?
Two new sets of chromosomes assemble at each pole of the cell
The nuclear envelope reforms around these chromosomes
The chromosomes begin to uncoil and the nucleolus is formed
Cytokinesis begins
What happens in cytokinesis in animal cells?
- Cleavage furrow forms around the middle of the cell
- Cytoskeleton pulls cell surface membrane inwards until it is close enough to fuse around the middle, forming two cells
What happens in cytokinesis in plant cells?
Vesicles gather along the middle of the cell and fuse with one another and the cell surface membrane, eventually the cell divides, forming two separate cells
What are homologous chromosomes?
Homologous chromosomes are chromosome pairs (one from each parent) that are similar (e.g. in length)
Overview of meiosis 1
The first division is the reduction division when the pairs of homologous chromosomes are separated into two cells- each will contain 23 chromosomes
What is the name for cells with only 23 chromosomes?
Haploid
Overview of meiosis 2
Similar to mitosis- the pairs of chromatids present in each cell are separated, forming two more cells (4 total overall)
What is the main thing that occurs in prophase 1 of meiosis?
Crossing over, where homologous chromosomes pair up and trade genes, forming bivalents
What is the main thing that occurs in metaphase 1 of meiosis?
Homologous pairs together assemble along the metaphase plate equator, contrary to in mitosis where they line up individually
What is independent assortment?
Where the orientation and location of each homologous pair on the metaphase plate equator is random and independent of any other homologous pair, meaning there are many different combinations that can occur
What does independent assortment result in?
Genetic variation
What are the main difference between anaphase 1 in meiosis and anaphase in mitosis?
In anaphase 1, homologous chromosomes are pulled to opposite poles, and chromatids stay joined to each other, whereas in anaphase in mitosis, the individual chromatids are pulled apart
What does diploid mean?
2 sets of chromosomes (46)
What happens to the number of chromosomes during prophase?
They remain the same, however each DNA molecule (aka chromosome) is converted into two identical chromatids
What happens in telephase 1 of meiosis?
- Nuclear membrane reforms around each group of chromosomes
- Cell undergoes cytokinesis
What happens to the number of chromosomes following meiosis 1?
Goes from one diploid cell to two haploid cells
What is meiosis 2 similar to?
Mitosis
What are the 4 final products of meoisis?
4 non identical haploid daughter cells
What are erythrocytes also known as?
Red blood cells
Erythrocytes properties (3)
- Flattened biconcave shape
- No nuclei or many other organelles
- Flexible
Why do erythrocytes have a flattened biconcave shape?
Increase surface area to volume ratio - transports oxygen around the body more efficiently
Why do erythrocytes have no nuclei or many other organelles?
`Increases space available for haemoglobin
Why are erythrocytes flexible?
Can squeeze through narrow capillaries
What are neutrophils?
A type of white blood cell
Neutrophils properties (3)
- Essential role in immune system
- Multi-lobed nucleus
- Granular cytoplasm contain many lysosomes
Why do neutrophils have a multi-lobed nucleus?
Can squeeze through small gaps to get to the site of infection
Why do neutrophils have many lysosomes?
Lysosomes contain enzymes used to attack pathogens
Sperm cells properties (3.5)
- Function is to deliver genetic information to the female gamete
- Flagellum/tail and many mitochondria
- Head of sperm contains digestive enzymes
Why do sperm cells have a flagellum/tail?
Flagellum makes them capable of movement, and mitochondria provide energy needed to move/swim
Why do sperm cells have digestive enzymes in their head?
To break down the protective layers of the egg, allows penetration and fertilisation
Palisade cells properties (5)
- Present in mesophyll
- Contain chloroplasts
- Thin walls
- Large vacuole
- Chloroplasts can move within the cytoplasm
Why do palisade cells contain chloroplasts?
To absorb large amounts of light for photosynthesis
Why do palisade cells have thin walls?
To increase rate of diffusion of CO2
Why do palisade cells have a large vacuole?
To maintain turgor pressure
Why can chloroplasts within the cytoplasm of palisade cells move?
To absorb more light
Root hair cells properties (2)
- Present at surfaces of roots near growing tips
- Have long extensions called root hairs
Why do root hair cells have root hairs?
To increase the surface area to volume ratio of the cell, which maximises the uptake of water and minerals from the soil
Guard cells properties
- Pairs of guard cells on the underside surfaces of leaves form small openings
- Cell wall thicker on one side than the other
- Change shape depending on water/K ion levels
What are the small openings between guard cells known as?
Stomata
What do guard cells control?
The entry of CO2, and the exit of water and oxygen
Where are stomata found and why?
On the underside of plant leaves, to reduce their exposure to heat and air current
How and why do stomata become turgid?
When the concentration of K ions within guard cells are high, water diffuses into the cells by osmosis, causing the cells to become turgid and have a large stomatal opening for CO2 to enter
How and why do stomata become flaccid?
When the concentration of K ions within guard cells are low, water diffuses out of the cells by osmosis, causing the cells to become flaccid and the stomatal opening closes- this is to prevent further loss of water from the plant.
Also stomata close at night, as CO2 is not needed as photosynthesis is not occuring
What is the effect of one cell wall being thicker than another in guard cells?
The cell does not change shape symmetrically as its volume changes
What are tissues?
Made up of a collection of differentiated cells that have a specialised function/functions. As a result each tissue is adapted for a particular function
What are the four main categories of tissues in animals?
- Nervous tissue- adapted to support the transmission of electrical impulses
- Epithelial tissue- adapted to cover internal and external body surfaces
- Muscle tissue- adapted to contract
- Connective tissue- adapted to either hold tissues together or as a transport medium
What is squamous epithelium also known as?
Pavement epithelium
Where do you find squamous epithelium?
Lining of the lungs
Why is squamous epithelium very thin?
Due to the flat cells that make it up, and because it is just one cell thick
What is the function of squamous epithelium?
To allow for rapid diffusion
What is squamous epithelium made up of?
Specialised squamous epithelial cells
What is ciliated epithelium made up of?
Specialised ciliated epithelial cells
What are cilia?
Hair like structures found on ciliated epithelial cells, that move in a rhythmic manner, causing (in the respiratory tract) mucus, dust and bacteria to be swept away
What do goblet cells do?
Release mucus, which traps any unwanted particles, which may be bacteria, from entering the lungs/alveoli
What type of tissue is cartilage?
Connective tissue
Where is cartilage found?
Outer ear, nose and ends/between bones
What fibres does cartilage contain?
Fibres of the proteins elastin and collagen
What is cartilage made up of?
Chondrocyte cells embedded in an extracellular matrix
What is the function of cartilage?
Prevents bones rubbing together and causing damage
What is the function of muscle?
Shortens in length (contracts) to move bones
What is skeletal muscle tissue?
Muscles attached to the bone
What is epidermis?
- Single layer of closely packed cells covering the surface of plants
- Usually covered by waxy, waterproof cuticle
- Contain stomata
What is vascular tissue in plants?
Adapted for transport of water and nutrients
What is xylem tissue?
- Vascular tissue
- Responsible for transport of water and minerals throughout plants
What is the purpose of lignin?
Waterproof material that strengthens the xylem tissue in plants
What are vessel elements?
Elongated dead cells
What is phloem tissue?
- Vascular tissue
- Responsible for transport of organic nutrients from photosynthesis to where it is needed in plants
What is xylem tissue made up of?
Vessel elements (elongated dead cells)
What is phloem tissue made up of?
Columns of sieve tube cells separated by sieve plates
What is an organ?
A collection of tissues that have been adapted to perform a particular function in an organism
Example of organ in plants
Leaf- made up of vascular and epidermis tissue- adapted for photosynthesis
What are organ systems?
Composed of a number of organs working together to carry out a major function
The digestive system functions (4)
- Takes in food and breaks down large insoluble molecules into small soluble ones
- Absorbs nutrients into the body
- Retains water needed by the body
- Removes any undigested material from the body
The cardiovascular system functions (2)
- Moves blood around the body
- Provides a transport system for substances to be transported around the body (e.g. oxygen)
The gaseous exchange system function
- Brings air into the body so oxygen can be extracted and carbon dioxide expelled
What stage of meiosis is reduction division?
Meiosis 1
Do all cells in plants and animals begin differentiated?
No, all cells begin undifferentiated
What does undifferentiated mean and what are these cells known as?
They are not adapted to any particular function, and have the potential to differentiate to become a specialised cell. These cells are called stem cells
What is potency?
A stem cell’s ability to differentiate into different cell types
What are the 3 different types of potency?
- Totipotency
- Pluripotent
- Multipotent
What are totipotent stem cells?
They can differentiate into any type of cell
Example of totipotent cell
Very early embryonic stem cells
What pluripotent stem cells?
They can differentiate into any tissue cell type
3 sources of stem cells in animals
- Embryos
- Umbilical cord
- Bone marrow
After how long do embryonic stem cells become pluripotent?
7 days
What is a blastocyst?
The mass of cells that form after 7 days after embryo production, turning the stem cells pluripotent
Where are all blood cells derived from?
Stem cells in the bone marrow
How could stem cells be used to treat heart disease?
Muscle tissue in the heart that has been damaged can be replaced and repaired by stem cells
How could stem cells be used to treat Parkinson’s disease?
Some symptoms are caused by the death of dopamine producing cells- these can be replaced by stem cells
3 areas in which stem cells are already being used
- Treatment of burns- stem cells can produce new skin
- Drug trials- drugs can be tested on cultures of stem cells
- Developmental biology- can be studied to improve knowledge on how organisms grow
Source of stem cells in plants
Meristems are pluripotent throughout the life of the plant, and are found in meristematic tissue
