B4 - Using food and controlling growth Flashcards
What is respiration?
A process that releases energy in the
form of ATP from the breakdown of
glucose
What is ATP?
It is a short term energy store in all cells
and is described as the universal energy
carrier.
Why does respiration occur continuously
in living cells?
ATP is required for many essential
processes in living cells e.g. movement,
homeostasis and active transport.
What type of reaction is respiration?
It is an exothermic reaction that releases
energy in the form of heat.
Where do plants get the glucose
required for respiration?
They produce their own glucose during
photosynthesis.
Where do animals get the glucose
required for respiration?
From the breakdown of carbohydrates
that they have ingested
What is aerobic respiration?
Respiration in the presence of oxygen
that forms ATP from the breakdown of
glucose
Write the word equation for aerobic
respiration
glucose + oxygen → carbon dioxide + water (+ATP)
Write the symbol equation for aerobic
respiration
C6H12O6 + 6O2 → 6CO2 + 6H2O (+ATP)
What does aerobic respiration require?
Glucose, C6H12O6
Or another respiratory substance e.g. lipids, proteins
Oxygen gas, O2
What does aerobic respiration produce?
Carbon dioxide gas, CO2
Water, H2O
ATP
Where does aerobic respiration take
place in eukaryotic cells?
In the cytoplasm and mitochondria
Where does aerobic respiration take
place in prokaryotic cells?
In the cytoplasm
What is anaerobic respiration?
Respiration that takes place without
oxygen and forms ATP from the
breakdown of glucose
When may anaerobic respiration take
place in human cells?
During vigorous exercise
When may anaerobic respiration take
place in plant cells?
If the soil becomes waterlogged
When may anaerobic respiration take
place in bacteria?
When bacteria enter puncture wounds
little oxygen available
Where does anaerobic respiration take
place?
It takes place in the cytoplasm of
eukaryotic and prokaryotic cells.
What does anaerobic respiration
require?
Glucose, C6H12O6
Or another respiratory substance e.g. lipids, proteins
Write the word equation for anaerobic
respiration in muscle cells
glucose → lactic acid (+ ATP)
Why may anaerobic respiration in
muscle cells eventually stop?
Lactic acid build-up inhibits anaerobic
respiration
What are the symptoms of lactic acid
build-up?
Cramp and fatigue
Write the word equation for anaerobic
respiration in yeast cells
glucose → ethanol + carbon dioxide
+ATP
What is the problem associated with
ethanol build-up in yeast cells?
Ethanol is toxic to yeast cells
Is aerobic or anaerobic respiration more
efficient? Explain why
Aerobic respiration is more efficient as it
produces 32 molecules of ATP in
comparison to anaerobic respiration
which produces 2 molecules of ATP.
Why does anaerobic respiration release
less energy than aerobic respiration?
Glucose is only partially broken down in
anaerobic respiration.
What is magnification?
The number of times bigger an image
appears compared to the size of the
specimen
How can the total magnification of an
image be calculated from lens powers?
total magifcation = eyepiece lens magnification X objective lens magnification
How can the magnification of an image
be calculated?
magnification = size of image / size of specimen
What is resolution?
The smallest distance between two
distinct objects that can be distinguished
How does a light microscope work?
A light microscope passes a beam of light
through a specimen. The light then travels
through the eyepiece lens, allowing the
specimen to be observed.
What are the advantages of light
microscopes? (4)
● Inexpensive
● Easy to use
● Portable
● Observe both dead and living specimens
What is the disadvantage of light
microscopes?
Limited resolution
How does an electron microscope work?
It uses a beam of electrons focused
using magnets. The electrons hit a
fluorescent screen which emits visible
light, producing an image.
Name the two types of electron
microscopes
Transmission electron microscope (TEM)
Scanning electron microscope (SEM)
What is the advantage of electron
microscopes?
Greater magnification and resolution
Why do electron microscopes have a
greater magnification and resolution?
They use a beam of electrons which has
a shorter wavelength than photons of
light
How have electron microscopes enabled
scientists to develop their understanding
of cells?
● Allow small sub-cellular structures (e.g. mitochondria,
ribosomes) to be observed in detail
● Enable scientists to develop more accurate
explanations about how cell structure relates to function
What are the disadvantages of electron
microscopes?
● Expensive
● Large so less portable
● Require training to use
● Only dead specimens can be observed
How do you convert from m to mm?
× 1000 (× 103
)
How do you convert from m to μm?
× 1 000 000 (× 106)
How do you convert from m to nm?
× 1 000 000 000 (× 109
)
How do you convert from m to pm?
× 1 000 000 000 000 (× 1012)
What is the cell cycle?
● A series of events that take place in a cell
involving cell growth, DNA replication and
cell division
● It is described as the lifecycle of a cell
State the two stages of the cell cycle
Stage 1 - interphase
Stage 2 - mitosis
What is interphase?
The longest stage of the cell cycle that
involves cell growth, the synthesis of
new organelles and DNA replication
What does DNA replication involve?
● Double helix ‘unzips’ exposing two strands
● DNA bases align next to complementary bases on
the DNA strands
● Complementary base pairs join
● Two identical DNA molecules formed
What is mitosis?
A form of cell division that produces two
genetically identical ‘daughter’ cells with
the same number of chromosomes
Why is mitosis important in organisms?
Mitosis is important for:
● Asexual reproduction
● Growth
● Repair of damaged cells
● Cell replacement
Describe the stages of mitosis
● Chromosomes line up along the cell equator
● Spindle fibres pull the two arms of each chromosome to
opposite poles of the cell
● Nucleus of the cell divides
● A new membrane forms around each set of chromosomes
● Cell divides producing two identical daughter cells
A cell divides by mitosis once every 2
minutes. Calculate the number of
identical cells present after 10 minutes.
10 ÷ 2 = 5
5 cell divisions have taken place
2^5= 32 cells
What is cancer?
● Non-communicable disease
● Uncontrolled cell division (due to damaged DNA) results
in the formation of a primary tumour
● Tumour cells break off and spread to other tissues
forming secondary tumours
What is a non-communicable disease?
A disease that is not spread between
organisms
What is sexual reproduction?
● Type of reproduction
● Involves the production of gametes by meiosis
● A gamete from each parent fuses to form a zygote
● Genetic information from each gamete is mixed so the
resulting zygote is genetically different from each parent
What are gametes?
● Sex cells (sperm cells, egg cells)
● Contain half the chromosome number
What is meiosis?
A form of cell division involved in the
formation of gametes where chromosome
number is halved. It involves two divisions.
What must occur prior to meiosis?
Interphase
What happens during the first stage of
meiosis?
The pair of chromosomes are separated
and move to opposite poles of the cell.
Chromosome number is halved.
What happens during the second stage
of meiosis?
The arms of each chromosome are
separated and move to opposite poles of
the cell. Four genetically different
gametes are produced.
Why is meiosis important for sexual
reproduction? (2)
● It increases genetic variation
● It ensures that the resultant zygote has
a full set of chromosomes
What are stem cells?
Cells that are unspecialised and capable
of differentiating into a range of different
cell types
What is meant by ‘differentiation’?
● A process in which stem cells become specialised
(have a specific function)
● Some genes switch on or off, determining cell
type
Why is cell differentiation important?
It enables the formation of specialised
tissues with specific functions e.g.
muscle tissue.
What are embryonic stem cells?
Stem cells found in very early embryos
that are unspecialised and capable of
differentiating into any cell type
When do embryonic stem cells begin to
differentiate?
After the eight cell stage
What is the function of embryonic stem
cells?
They enable the growth and
development of tissues in human
embryos.
What are adult stem cells?
Stem cells that can differentiate into a
limited range of cell types e.g. bone
marrow stem cells
What is the primary function of adult
stem cells?
Replacement of dead cells e.g.
replacement of red blood cells which
only live for 120 days
Where are stem cells found in plants?
Meristems
Where is meristem tissue found?
In regions of the plant where cells are
continuously dividing e.g. root tips, shoot
tips
What are meristematic stem cells?
Stem cells found in meristems that are
unspecialised and capable of
differentiating into any cell type during
the life of a plant
What are plant tropisms?
The growth response of a plant to a
stimulus
What is positive tropism?
The growth of a plant towards a stimulus
What is negative tropism?
The growth of a plant away from a
stimulus
What are the two main types of plant
tropism?
Phototropism
Gravitropism
Define phototropism
A plant’s growth response to light
Define gravitropism
A plant’s growth response to gravity
What are auxins?
● A group of plant hormones involved in plant
tropisms
● Control growth in plant roots and shoot tips
Compare the effect of auxins in plant
shoots and roots
Auxins stimulate growth in plant shoots
Auxins inhibit growth in plant roots
Where are auxins produced?
Root and shoot tips
How do auxins move through a plant?
They diffuse through the plant in solution
Are plant shoots positively or negatively
phototropic? How does this affect shoot
growth?
● Positively phototropic
● Plant shoots grow towards the light
Explain why plant shoots are positively
phototropic
● Shoot tip exposed to light
● On the shaded side of the root, auxin accumulates
● Elongation of cells on the shaded side
● Shoot tip bends towards the light
Are plant shoots positively or negatively
gravitropic? How does this affect shoot
growth?
● Negatively gravitropic
● Plant shoots grow upwards, away from
gravity
Explain why plant shoots are negatively
gravitropic
● Shoot placed horizontally
● Due to gravity, auxin accumulates on the lower side of
the shoot
● Elongation of cells on the lower side
● Shoot bends upwards growing away from gravity
Are plant roots positively or negatively
phototropic? How does this affect root
growth?
● Negatively phototropic
● Plant roots grow away from the light
Explain why plant roots are negatively
phototropic
● Root exposed to light
● On the shaded side of the root, auxin accumulates
● Inhibition of cell growth on the shaded side
● Root grows away from the light
Are plant roots positively or negatively
gravitropic? How does this affect root
growth?
● Positively gravitropic
● Plant roots grow downwards, towards
gravity
Explain why plant roots are positively
gravitropic
● Root placed horizontally
● Due to gravity, auxin accumulates on the lower side of
the root
● Inhibition of cell growth on the lower side
● Root bends downwards growing towards gravity
Explain how plant tropisms increase the
chance of survival
● They enable plants to respond to their environment
● Shoot growth towards the light maximises light absorption
● Root growth downwards increases the uptake of water
and minerals from the soil and enables anchorage of the
plant body to the ground
Describe the role of auxins in
commercial plant cultivation
● Rooting powders contain auxins
● Auxins stimulate the growth of roots in cuttings
● Enables rapid plant cloning
What are gibberellins?
Plant hormones that control germination
and flowering
How do gibberellins trigger germination?
In the presence of water, gibberellins
break seed dormancy, initiating
germination.
What is ‘bolting’ in plants?
● In response to a period of low temperatures or limited
water availability
● Flowering and seed production increase in a final bid
for a plant to reproduce before death
● Triggered by gibberellins
Why are gibberellins important in
commercial plant cultivation?
● Applied to seeds to make them germinate at times of the year when
they naturally wouldn’t
● Makes sure all seeds germinate at the same time
● Initiate flowering in plants at any time of the year
● Enable flowering under conditions in which plants would normally not
● Can increase fruit size
What effect does ethene have on plants?
● Causes dead leaves to drop off a plant by
triggering the expansion and bursting of cells in
leaf stalks
● Stimulates enzymes that control fruit ripening
Why is ethene important in commercial
plant cultivation?
● Used to remove the dead leaves from plants, aiding
the collection of fruits and seeds
● Enables fruits to be picked while they are unripe and
less easily damaged. They can be stimulated to ripen
during transportation to shops.
How can stem cells be used in
medicine?
● Stem cells collected
● Stem cells stimulated to differentiate into specific
cell types e.g. heart muscle cells
● Specialised cells transplanted into the patient
● Used to treat damage or disease e.g. heart disease
Where can embryonic stem cells be
collected from?
● Donor stem cells removed from
embryos grown in vitro
● Patient’s own stem cells removed from
the umbilical blood before birth
What are the benefits of using stem cells
in medicine?
● Treat damage or disease e.g. heart disease, type 1 diabetes
● Treat diseases that would otherwise be untreatable
● Used in scientific research
● Growing organs for transplants
What are the risks of stem cell use in
medicine?
● Transplanted stem cells could cause tumours
● Finding suitable stem cell donors is a difficult task
● Stem cells may be rejected by the body (immunosuppressants taken)
● Potential side effects
● Long term risks of using stem cells are unknown
● Stem cells may become contaminated during preparation and when
transplanted, transmit infections to the patient, making them sicker
What are the ethical issues related to the
use of stem cells in medicine?
● The embryos used to provide stem cells are
destroyed which is seen as unethical and a waste
of potential human life
● May lead to the reproductive cloning of humans
