Cells And Control Flashcards
Which two ways can a cell divide and reproduce?
Mitosis and meiosis
What’s asexual reproduction of cells? What do they produce?
Mitosis.
Asexual reproduction involves only one parent. The offspring have identical genes to the parent with no variation between parent and offspring.
Mitosis
When a cell reproduces itself by splitting to form 2 cells with identical sets of chromosomes.
Chromosomes
Coiled up lengths of DNA molecules
How many copies of each chromosome do diploid cells have? Where do these come from?
2, one from the father (Y) and one from the mother (X)
What’s the cell cycle and what’s its function?
When body cells in a multicellular organism divide to produce new cells. Mitosis is part of this and is used for growth and repair of cells that have been damaged, they can also be used in some organisms to reproduce.
What’s interphase? Is it a stage of mitosis?
Interphase isn’t a phase of mitosis. Before division, the cell has to grow and increase the amount of sub-cellular structures. The DNA is then duplicated and copied to form ‘X shaped chromosomes’ with each arm the exact duplicate of the other.
What’s the first stage of mitosis?
Prophase, chromosomes condense (getting shorter and fatter). Nuclear membrane breaks down so that chromosomes are free in the cytoplasm. Spindles start to appear.
When do spindles start to appear?
Prophase
What’s the second stage of mitosis?
Metaphase, the chromosomes line up in the middle of the cell with microtubules connected to each centromere.
What are chromatids joined together by?
A centromere
What are spindle fibres called?
Microtubules
What’s the third stage of mitosis?
Anaphase, centromeres split and each chromatid is dragged by the spindle fibres to opposite ends of the cell.
What’s the fourth stage of mitosis?
Telophase, the group of chromatids assemble at both ends and spindle fibres disintegrate while the nuclear membrane forms around them. They then lengthen and uncoil into chromatin. A crease called a cleavage forms in the middle of the cell.
Cytokinesis
The splitting of the cell membrane to form 2 diploid cells.
What processes does growth in plants involve?
Cell division, differentiation and elongation
Growth
Increase in dry mass of a plant/animal.
Cell differentiation
Process by which a cell changes to become specialised for its job. Specialised cells allows multicellular organisms to act more efficiently.
Cell elongation
Where a plant cell expands, making the cell bigger and so making the plant grow.
How does animal growth work?
Cell division. Animals grow when young and then reach full growth and stop. Younger animals’ cells divide at fast rates for growth while adult’s cell division is mostly for repair and replacement of old/damaged cells. CELL DIFFERENTIATION IS LOST AT AN EARLY AGE.
How does plant growth work?
Cell division usually occurs in the tips/ roots of a cell (meristem) and then elongate throughout due to water absorption. Their growth happens continuously and they differentiate throughout its lifetime.
Meristem
Cells found in growing areas of the plant such as roots and shoots that produce unspecialised cells, due to carrying out mitosis, that can be any cell within the plant. Unspecialised cells go on to form specialised tissues like xylem/phloem
What controls mitosis rate?
The chemical instructions (genes) within an organism’s DNA. If there’s a change / mutation within a gene, cells may start dividing UNCONTROLLABLY. This results in a tumour.
Tumour
Mass of abnormal cells, if it in cases and destroys surrounding tissues, it is cancer.
What’s the hayflick limit?
The limit applied to the maximum number of times a cell can divide (50 on average).
What can make monitor growth? Why?
Percentile charts create an overall pattern of development that can be observed and checked for problems/ inconsistent patterns.
What would the 50th percentile show?
The top 50%
How do they measure a child’s growth?
Mass, length and head circumference
Stem cells
Undifferentiated cells
Where are embryonic stem cells found?
In human embryos. These embryonic stem cells can differentiate into any cell at all.
Why are stem cells important to organisms?
They are essential to growth and development of organisms.
Where are adult stem cells found?
Bone marrow, they aren’t as versatile as embryonic as embryonic cells as they can only differentiate into certain cells. In adults, they are used to replace damaged cells.
How are stem cells used in medicine?
ADUULT stem cells cure some diseases such as sickle cell anaemia as adult stem cells can produce new blood cells. There’s much potential regarding disease curing.
EMBRYONIC stem cells have been produced in labs and stimulated into specialised cells but the embryo has to be destroyed after 2 weeks.
In the future, it could be possible to replace damaged/ diseased cells in a transplant of embryonic stem cells grown into that tissue/organ.
Much research needs to be done.
What are the disadvantages of embryonic stem cells?
Ethical problems,
have to be destroyed after 2 weeks,
Inability to control growth could result in cancer,
Could transmit diseases,
Could be rejected,
Drugs taken to repress rejection weaken immune system
Disadvantages of adult stem cells?
Can produce cancer,
Can be rejected,
Can transmit disease,
Not as potent as embryonic,
Arguments for embryonic stem cells
Suffering is more important than lives of embryos,
Embryos used are usually unwanted ones from fertility clinics,
Why plants/ animals respond to changes in their external environment?
To increase chances of survival
Why do animals respond to changes in their internal environment?
To make sure that conditions are always right for METABOLISM.
Stimulus
Any change in the internal/external environment
Function of receptors
They DETECT STIMULI. Receptors within the sense organs detect external stimuli.
What’s the function of effectors?
Cells that bring about a response to stimuli through cells like muscles (contraction) and glands (secrete hormones).
How do receptors communicate with effectors?
The nervous system/ hormonal system
What’s the nervous system made up of?
All the neurones in your body.
What are the three main types of neurone?
Sensory, relay and motor
What does the central nervous system (CNS) consist of? What’s its function?
The brain and spinal chord only. Its function is to coordinate responses to stimuli due to high speed electrical impulses that are sent to effectors along a motor neurone rapidly.
What happens when receptors detect stimulus?
The info is converted to electrical impulses which are sent along sensory neurones to the CNS.
Synapse and its function.
The connection between 2 neurones. Transfers nerve signals via neurotransmitters which diffuse across the gap and set off a new electrical signal in the next neurone. They stop the rate of electricity from flowing backwards.
4 main areas of the brain
Cerebrum, cerebellum, medulla oblongata and hypothalamus
Function of cerebrum
Controls memory, language, vision, intelligence and movement. Is largest part of brain.
Function of cerebellum
Controls balance and muscle coordination.
Function of medulla
Controls heart and breathing rate (subconscious internal activity )
Function of hypothalamus
Regulates temperature and water balance
What is the cerebrum split into?
The left and right hemispheres. The right hemisphere controls muscles on the left side of the body (vice versa).
What is the size of sensory area proportional to?
Relative number of receptive body cells in body part.
How do receptors communicate with the CNS?
Sensory neurones
How does the CNS communicate with effectors?
Motor neurones
How have neuroscientists mapped out various regions of the brain for different functions?
Studying brain damage patients, electrical stimulation of different parts of the brain, taking MRI scans (magnetic resonance imaging)
What are the risks associated with treatment of brain diseases?
Surgery may do more damage/ create side effects to the patient due to the difficulty of such a procedure. These may affect a patient’s quality of life.
It’s hard to obtain consent from brain damaged people.
What are the three modern techniques scientists use to scan brains?
Magnetic resonance imaging (MRI), positron emission tomography (PET) or computer tomography (CT).
Spinal chord and its function
A long column of neurones that run from the base of the brain down the spine. It’s function is to relay information between the brain and the rest of the body.
What scanners are used to investigate brain function?
Computer Tomography (CT scan) Positron Emission Tomography (PET scan)
How does a CT scan work?
Uses X rays to produce a 2D image of the brain, processed by computer to be 3D.
How do PET scans work?
They use radioactive chemicals to show which parts of the brain are active when person is inside scanner. V detailed and can be used to investigate structure/function of brain and disorders that change brain activity such as Alzheimer’s disease.
Why is it hard to treat CNS problems?
Because neurones in the CNS don’t readily repair themselves and scientists are yet to do more research.
Problems are difficult to access, for example some brain tumours are unreachable so have to be treated using ways like chemo or radio therapy.
It’s also v risky to treat as can cause permanent damage.
Neurones
Nerve cells that are adapted to send electrical impulses from one place to another. Eg:
SENSORY
RELAY
MOTOR
Neurotransmission
Travel of impulses
Effectors
Muscles/glands
What are the characteristics of all neurones?
They all have a cell body with a nucleus. The cell body has extensions connecting to other neurones. They all have dendrons/axons.
Where do dendrons carry nerve impulses?
Towards the cell body
Where do axons carry nerve impulses?
Away from the cell body.
Function of myelin sheath
Acts as an electrical insulator which speeds up the travel of impulses.
Advantage of having long neurones
Impulse is sped up due to lack of connections which would slow the impulse down.
Sensory neurone characteristics
One long dendron that carries nerve impulses from receptors to cell body. The cell body is central of the neurone. A short axon carries nerve impulses from the cell body to the CNS.
Where do sensory neurones carry nerve impulses?
From receptors to cell body to CNS.
Characteristics of a motor neurone
Many short dendrites carry nerve impulses from CNS to cell body. Long axon carries them then on to the effector cells.
Characteristics of a relay neurone?
Many short dendrites carry impulses from sensory neurones to cell body. Axon carries them from the cell body and then on to the motor neurones.
Where do motor neurones carry impulses?
From the CNS to cell body and then onwards to effectors.
Where do relay neurones carry impulses?
From sensory neurones to cell body and onwards onto motor neurones.
Synapse
The connection between two neurones.
How do synapses work?
Chemicals called neurotransmitters are held in bags which are opened by electrical impulses diffuse across the gap between neurones and are absorbed by receptors and fuse to the next neurone. This the. Sets off an electrical signal in the next neurone.
Functions of the synapse
Stops the electricity from going the wrong way.
Filters out any unimportant info.
What types of energy are involved in transmission
Electrical>chemical>electrical
Reflexes and functions.
Automatic, rapid responses to stimuli. Function is to prevent injury.
Reflex arc
Passage of info in a reflex (from receptor to effector).
Stages of the reflex arc
- ) a change in stimuli is detected by a receptor.
- ) the info from the receptor is translated to electrical signals in the sensory neurone and up to the relay neurone.
- ) the impulse reaches a synapse between the sensory neurone and the relay neurone, neurotransmitters enables the transmission onto the relay neurone.
- ) the relay neurone reaches another synapse between the relay/motor and the same occurs.
- ) the impulses then travel along the motor neurone to the effector.
- ) the reflex happens
What reflex does the eye carry out?
Light receptors on the eye detect v bright light and so send a message along the sensory neurone to the brain, this then travels along the relay neurone to the motor neurone. The motor neurone tells the circular muscles (effectors) in the iris which makes the pupil smaller so that the eye isn’t damaged by bright light.
Function of the cornea
Transparent outer layer at front of the eye which refracts light into the eye.
Function of the iris
Controls how much light enters the pupil via muscles that control the diameter of the pupil.
(Coloured area around pupil)
Function of the lens
Refracts light and focuses it on the retina. Is elastic so can focus light on retina by changing shape.
Function of the retina
Sensitive to light an holds receptor cells called rod and cones which detect light.
Rods function
More sensitive in dim light but can’t sense colour
Cone receptor cell functions
Sensitive to different colours but aren’t good in dim light.
Function of optic nerve
Carries electrical impulses from rod and cone cells to brain.
What does your eye do to focus on distant objects?
The ciliary muscle relaxes and allows suspensores ligaments to pull tight which pulls the lens into a less rounded shape so light is refracted less.
What does your eye do to look at close things?
The ciliary muscle contracts to slacken the suspensorio ligaments and create a more rounded shape to refract the light more.
Sclera
The tough supporting wall of the eye.
Ciliary muscles/ suspensory ligaments
Control the shape of the lens
Accommodation
Changing the shape of the lens to focus light on the retina.
What are longsighted people unable to do?
Focus on near objects
What is longsightedness?
When the lens is the wrong shape and so doesn’t refract the light enough or the eyeball is too short. This means that light from near objects are focused behind the retina.
How do you correct longsightedness?
Wearing glasses/contact lenses with a convex lens.
What are shortsighted people unable to do?
Focus on far objects.
What is shortsightedness?
When the lens is the wrong shape and so refracts the light too much or that the eyeball is too long. This means that light from distant objects are brought into focus in front of the retina.
How do you correct shortsightedness?
Wear glasses / contact lenses with a concave lens.
What’s color blindness and how do you cure it?
When you cant tell the difference between different colours (eg:red-green) due to cone receptor cells not working properly. There’s no cure for this as cone cells can’t be replaced.
What are cataracts and how are they cured?
It’s a cloudy patch on the lens which stops light from being able to enter the eye normally and so create blurred vision and less colour vividness. This can be solved by replacing the faulty lens with an artificial one.
