Transcript B2 Revision Presentation

Biology
Unit 2 – Topic 1
The building blocks of cells
Bacteria
Chromosomal DNA is a giant loop
of DNA containing most of the
genetic material.
Bacteria
Plasmid DNA comes in small loops
and carries extra genetic
information.
Bacteria
The flagella, if there is one, is on the
outside of the bacteria cell. These are
long, whip-like structures to move
the bacteria along.
Bacteria
The cell wall does a similar job to a
plant cell wall but it is different.
It is more flexible and it is not made
from cellulose.
Plant cell only
Chloroplasts contain the green
pigment called chlorophyll. This
absorbs light energy for
photosynthesis.
Plant cell only
The large vacuole is a space in the
cytoplasm that is filled with cell sap.
This helps to support the plant by
keeping the cells rigid.
Plant cell only
The cell wall is made of cellulose to
support the cell and to keep its
shape.
Plant and animal cell
The cell membrane controls the
movements of substances like
oxygen, carbon dioxide and glucose
into and out of the cell.
Plant and animal cell
Mitochondria are very small
organelles in which respiration
occurs.
Plant and animal cell
The cytoplasm is where many of the
chemical reactions that take place.
Plant and animal cell
The nucleus contains the DNA. It
controls all the activities of the cell.
Light microscope
The best light microscopes can
magnify specimens more than 1500
times.
Electron microscope
These microscopes use a beam of
electrons to magnify the specimen
up to 2 million times. This lets us see
very clear and detailed structures
inside cells.
Gene
A gene is a section of a molecule of
DNA.
It codes for a specific protein.
DNA
A DNA molecule is two strands
coiled together to form a double
helix.
DNA
The two strands are linked
(like rungs on a ladder)
by a series of base pairs
joined together by
weak hydrogen bonds.
DNA Base Pairs
Adenine (A) pairs with thymine (T)
(so the pointy letters pair together)
Cytosine (C) pairs with guanine (G)
(and the curly letters pair together)
DNA Base Pairs
The order of bases in a section of
DNA decides the order of amino
acids in the protein
Genetic engineering
This is where scientists
remove a gene from one organism
and
insert it into the DNA of another
organism.
Advantages Genetic
engineering
Golden rice plants are normal rice
plants with 2 extra genes inserted so
that they make beta-carotene in the
grains. This is required in humans to
make Vitamin A
Advantages Genetic
engineering
The gene for human insulin is
inserted into bacterial plasmid DNA.
The genetically modified (GM)
bacteria can then make insulin. This
is used by people with Type 1
diabetes.
Advantages Genetic
engineering
Scientists have added genes to some plants to
make them herbicide resistant (weed-killer
resistant). This will reduce the amount of crop
spraying needed because the farmer can use one
large dose of the herbicide rather than lots of
smaller doses.
Mitosis
Most nuclei contain 2 copies of each
chromosome.
This makes the diploid cells.
Mitosis
Human diploid cells contain two sets
of 23 chromosomes.
Body cells (all cells except sperm
and egg cells) are diploid.
Mitosis
Body cells divide to make more
body cells or to replace damaged
cells by mitosis.
Mitosis
Mitosis occurs during growth, repair
and asexual reproduction.
Mitosis
Mitosis produces 2 daughter cells,
each with identical sets of
chromosomes in the nucleus to the
parent cell.
Mitosis
Mitosis results in the formation of
two genetically identical
diploid
body cells.
Fertilisation
At fertilization, haploid gametes
combine to form a diploid zygote.
Zygote
A zygote is a fertilized egg cell.
Meiosis
Meiosis is needed to produce
haploid gametes.
Meiosis
Meiosis makes four haploid
daughter cells, each with half the
number of chromosomes.
This results in genetically different
haploid gametes.
Mitosis or Meiosis
Me1osis for 1 set of chromosomes.
Mi2osis for 2 sets of chromosomes.
Alleles
Each chromosome in a pair contains
the same genes but may have
different versions of those genes
called alleles.
Clones
Clones are examples of asexual
reproduction that are genetically
identical copies of each other.
Stem cells
Stem cells in the embryo can
differentiate into all other types of
cells, but that cells lose this ability as
the animal matures.
Proteins
Proteins are made from amino acids.
Proteins
Different proteins have different
numbers of amino acids arranged in
different orders. This makes
different shaped molecules that have
different functions or jobs.
Proteins
Enzymes are proteins.
Gene mutations
Gene mutations change the DNA
base sequence and so can change the
protein.
Gene mutations
Gene mutations can harmful, have
no effect or be beneficial to the
organism.
Eg. Some mutations in bacteria make
them resistant to antibiotics.
Enzymes
Enzymes are Biological catalysts.
Enzymes
Enzymes catalyse chemical reactions
occurring inside and outside living
cells.
Enzymes
Enzymes catalyse:
DNA replication
Protein synthesis
Digestion
Enzymes
The molecules that enzymes work
on are called substrate molecules.
Enzymes
Enzymes are very specific and will
only work with a particular
substrate or a small group of
substances.
Enzymes
Enzymes are affected by:
Temperature
Substrate concentration
pH
Enzymes
Changing the pH or temperature
will change the shape of the active
site in the enzyme.
Too much change may break the
chemical bonds in an enzyme.
Denatured
Too many changes in the enzyme
will destroy the active site so the
enzyme will not work. The enzyme
has been denatured.
Enzymes
The model of how enzymes work is
called the
Lock and key hypothesis.
Biology
Unit 2 – Topic 2
Organisms and energy
Respiration
Respiration is a process used by all living
organisms that releases the energy in
organic molecules
Respiration
Glucose and oxygen diffuses from
capillaries into respiring cells.
Respiration
Carbon dioxide diffuses from respiring
cells into capillaries.
Diffusion
Diffusion is the movement of particles
from an area of higher concentration to an
area of lower concentration.
Aerobic respiration
Aerobic respiration
uses Oxygen
to release energy from glucose.
Aerobic respiration
Glucose + oxygen
carbon dioxide +water
The energy from the glucose is released for use
in the cell.
Exercise
Exercise can cause a change in heart and
breathing rates.
Exercise
During exercise the muscles use up oxygen and
glucose quickly, so the breathing rate increases
to get more oxygen and the heart beats faster to
pump more blood with more oxygen and
glucose to these cells.
Amount of blood
The cardiac output is the volume of blood
circulated by the heart in a given time.
Amount of blood
Cardiac output = stroke volume x heart rate
Amount of blood
Cardiac
output
Stroke
volume
Heart
rate
Anaerobic respiration
Sometimes, when we carry out vigorous
exercise we cannot supply enough oxygen to
the muscle cells so we start to respire
anaerobically.
Anaerobic respiration
Anaerobic respiration breaks down glucose and
releases energy without any oxygen.
Anaerobic Respiration
Glucose
lactic acid
The energy from the glucose is released for use
in the cell.
Anaerobic Respiration
Anaerobic respiration
releases less energy
than aerobic respiration.
Lactic acid
Lactic acid produced by anaerobic respiration
exercise may cause muscle cramps.
Lactic acid
After exercise increased oxygen is required to break
down the Lactic acid into carbon dioxide and water.
This need for extra oxygen after exercise is called
Excess post-exercise oxygen consumption.
(EPOC)
Photosynthesis
A leaf is adapted for photosynthesis.
Large surface area
Chlorophyll in chloroplasts to absorb light
Stomata for gas exchange
(carbon dioxide, oxygen and water)
Photosynthesis
Plants absorb light energy to make glucose.
Carbon dioxide + water
glucose + oxygen
Rate of photosynthesis
For photosynthesis to happen there must be
enough carbon dioxide, water, a suitable
temperature and light to give the energy for the
reactions. The one that is in the shortest supply is
called the limiting factor.
Water transport
Roots do more than just anchor a plant to the
ground. They take up water and dissolved nitrate
and other mineral ions from the soil.
Root hair cells
Root hair cells have long tin extensions that reach
into the nearby soil. This gives them a
bigger surface area
for the water and mineral ions to enter.
Water transport
Water enters the root hair cells by
osmosis.
Here, water moves across a
partially permeable membrane.
Osmosis
Osmosis is the movement of water molecules
from an area of higher concentration of water
to an area of lower concentration of water
through a partially permeable membrane.
Transpiration
This is the evaporation of water vapour from the
surface of a plant.
Transpiration
The loss of water from a leaf pulls water and
dissolved mineral salts up through the xylem from
the roots.
This process is called transpiration.
Active transport
Roots can absorb nitrates and other mineral ions
dissolved in soil water even if the concentration is
higher in the plant than in the soil water. Absorbing
particles against a concentration gradient is called
active transport. The energy for this comes from
repiration.
Xylem vessels
Xylem vessels transport water and dissolved
mineral salts up a plant.
Water Xylem
WX
Phloem vessels
The glucose made in the leaves by photosynthesis is
converted to sucrose and carried to other parts of
the plant by the phloem tissue.
Sampling techniques
A pooter is used to suck small invertebrates into a
tube.
Sampling techniques
A sweep net is used to drag through long grass to
catch any organisms. Similarly, a pond net could be
used for aquatic habitats.
Sampling techniques
A pitfall trap is a jar which small animals fall into
and are trapped.
Sampling techniques
A quadrat is a square frame placed at random place
on the ground and the plants in that area counted.
Sampling techniques
Environmental factors which could be measured
include:
Temperature
Light intensity
pH
B2 – Topic 3
Common systems
Fossils
Fossils are the preserved traces or remains
of organisms that lived thousands or millions of
years ago.
Fossil record
This is the collection of fossils
identified from different periods of time
that can be interpreted
to form a hypothesis
about the evolution of life on Earth.
Gaps in the Fossil record
There are gaps because:
1) fossils do not always form.
2) soft tissue decays
3) many fossils are yet to be found.
Growth
When organisms grow they get bigger.
The easiest way to observe growth is to
measure an increase in size, length or mass.
Percentile charts
These charts or graphs are used to compare a
certain characteristic (e.g. mass) against the
total population.
Plant growth
Growth in an organism involves two processes.
1) Cell division where one cell divides to form
two identical cells.
2) The cell gets longer by elongation.
Plant development
Plants grow all the time.
As the plant stem or root continues to grow
the older meristem cells start to become
specialised – they differentiate.
Animal development
Animals stop growing when they become
adults. In an animal, cells that can differentiate
to form a number of different types of
specialised cells are called stem cells.
Parts of the blood
Red blood cells
White blood cells
Plasma
Platelets
Parts of the blood
A red blood cell
has the shape of a biconcave disc.
This increases the surface area for diffusion.
Red blood cells
contain the red pigment haemoglobin.
Red blood cells have no nucleus.
Parts of the blood
White blood cells are part of the body’s defences
against disease. Some white blood cells make
antibodies. Other white blood cells surround and
destroy any foreign cells like bacteria that get into the
body.
White blood cells have a nucleus.
Parts of the blood
Plasma is a yellow liquid.
It transports dissolved substances, such as carbon
dioxide, food substances and hormones.
Parts of the blood
Platelets are tiny fragments of cells
(and so do not have a nucleus).
They are important in making your blood clot if
you cut or damage your blood vessels. The clot
dries out and forms a scab which stops microorganisms like bacteria getting into the body.
Cells, tissues, organs and systems
A group of the same specialised cells form a tissue.
e.g. muscle tissue is made from muscle cells.
Cells, tissues, organs and systems
An organ contains several different tissues
working together to carry out a particular job. The
heart is an organ that pumps blood to the lungs
and around the body.
Cells, tissues, organs and systems
Groups of organs that work together are called
organ systems.
e.g. the heart and blood vessels make an organ
system called the circulatory system.
Cells, tissues, organs and systems
Groups of organs that work together are called
organ systems.
e.g. the heart and blood vessels make an organ
system called the circulatory system.
The heart
The heart is an organ that pumps blood around
the body.
There are 4 major blood vessels associated with
the heart.
The heart
The pulmonary artery takes deoxygenated blood
to the lungs to get oxygen.
The pulmonary vein takes oxygenated blood back
from the lungs to the heart.
The heart
The aorta carries oxygenated blood around the
body.
The vena cava carries deoxygenated blood back to
the heart where it is pumped back to the lungs.
The heart
The left atrium and ventricle pump oxygenated
blood.
The heart
The right atrium and ventricle pump
deoxygenated blood.
The heart
Veins and the heart have valves to prevent
backflow – to stop the blood going the wrong way.
The heart
The muscle wall of the left ventricle is thicker than
the right ventricle because it has to pump blood all
around the body rather than just to the lungs.
The heart
The heart
• Arteries transport blood away from the heart.
• Arteries have strong, thick walls to withstand
the blood at high pressure.
The heart
• Veins transport blood to the heart.
• Veins are wide because the blood flows
relatively slowly under low pressure.
The heart
• Capillaries exchange materials with tissues by
diffusion so they have very thin walls.
The digestive system
• Food is broken down in the organ system
called the digestive system.
The digestive system
• In the mouth, teeth break up the food into
small pieces. This increases the surface area
for digestive enzymes to work on – like
amylase.
The digestive system
• The oesophagus is a muscular tube between
the mouth and stomach.
• Muscles contract in waves to push the food
down it – this is called peristalsis.
The digestive system
• The stomach is a bag that makes Hydrochloric
acid and some enzymes like pepsin to break
down proteins. It churns the food up.
The digestive system
• The small intestine is a long tube where most
of the large insoluble food molecules are
broken down into smaller soluble molecules.
There are lots of enzymes. Food is again
moved by muscles in peristalsis.
The digestive system
• The surface area of the small intestine is
greatly increases by having lots of finger like
projections called villi which contain
capillaries.
The digestive system
• Water diffuses back into the blood in the large
intestine leaving the waste material called
faeces behind.
The digestive system
• The pancreas make digestive enzymes and
releases them into the first part of the small
intestine.
The digestive system
• Digested food absorbed by the small intestine
is taken in the blood plasma to the liver. Here
some of the molecules are broken down even
more. Some are built up into larger molecules.
The liver also makes bile which helps in the
digestion of fats.
The digestive system – Higher paper
• The gall bladder is a small organ that stores
the bile made by the liver. It releases the bile
into the small intestine when it is needed.
The digestive system
Enzymes
• Carbohydrases are digestive enzymes that
break down carbohydrates into sugars.
• Amylase breaks down starch into sugar.
Enzymes
• Proteases are enzymes that break down
proteins into amino acids.
• Pepsin is an enzyme that breaks down
proteins in the stomach.
Enzymes
• Lipases are enzymes that break down fat
molecules into fatty acids and glycerol.
Bile – Higher paper
• Bile breaks down large globules of fat and oil
into tiny droplets forming an emulsion. The
smaller droplets have a larger surface area
which lets the lipase enzymes break down the
fat molecules quicker. Bile is also slightly
alkaline and so will neutralise the
Hydrochloric acid from the stomach.
Probiotics
• Probiotics contain live bacteria which maybe
helpful to the digestive system.
• These bacteria are usually Lactobacillus and
Bifidibacteria. They are found in yoghurts or
yoghurt drinks.
Prebiotics
• Prebiotics are substances that the body can’t
digest. They act as food for the probiotic
bacteria. Tomatoes, bananas, onions and
asparagus all contain oligosaccharides, a
common form of prebiotic.
Plant stanol esters
• Plant stanol esters are oily substances found
in plants. These can stop the small intestine
absorbing cholesterol so lowering the level of
cholesterol in the blood.
• Plant stanols are now used in many yoghurt,
drinks and spreads.