Biology paper 1 video notes
CELL BIOLOGY
Kingdoms of life:
- Eukaryotic cells: DNA is in the form of chromosomes or found in the nucleus.
Examples are animal cells, plant cells, and fungi.
- Prokaryotic cells: don’t have a nucleus, their DNA is loose in a cell and there may be
one or more small rings of DNA called plasmids. . They are also much smaller than
eukaryotic cells. An example is bacteria
Cell types and Cell structure:
- Cells are the smallest unit of life that can replicate independently.
- Organelles in both animal and plant cells:
Cell membrane - controls which substances can pass in and out of the cell
Nucleus - contains genetic material/DNA
Cytoplasm - where chemical reactions take place
Mitochondria - provides cells with energy they need to function (where respiration
happens)
Ribosomes - site of protein synthesis
- Plant cell only organelles:
Rigid cell wall - made up of cellulose which supports the cell
Permanent vacuole - contains cell sap
Chloroplasts - where photosynthesis happens. Also contains chlorophyll that makes
plants’ leaves green.
- Bacterial cells’ organelles: cytoplasm, cell wall, cell membrane and ribosomes.They
also have a circular strand of DNA which contains the genes they need to survive
and reproduce. They have plasmids with extra rings of DNA that carry extra genes
for antibiotic resistance.
Microscopy:
- Base at the bottom, then an arm, a type of light
source (lamp), stage which is where we put our
microscope slide, 3 objective lenses which have
different magnifications, eyepiece lens with a fixed
magnification so we can see into the microscope,
coarse and fine focusing knob which we can turn to
help get the image in focus.
- Resolution - the shortest distance between two points
on an object, that can still be distinguished as two
separate entities.
Light and electron microscopes:
- Light microscopes:
Easy to use, relatively cheap, however because they
rely on light, their resolution is limited to a very small number so any details less will
appear blurry.
, - Electron microscopes:
Very expensive, hard to use so only used by scientists in labs, uses electrons instead
of light so their resolution is very high.
Cell division:
- The nucleus contains your genetic information. This is found in the form of
chromosomes which contain DNA.
- A gene is a short section of DNA that codes for a protein.
- The cell cycle:
Stage 1 - the cell grows, organelles grow and increase in number. DNA is replicated.
- Stage 2 - the chromosomes line up at the equator of the cell and one set of
chromosomes is pulled to each end of the cell.
Stage 3 - the cytoplasm and cell membrane divide to form two identical daughter
cells.
Diffusion:
- Diffusion is the net movement of particles from an area of high concentration to an
area of low concentration through a semi permeable membrane.
- This is a passive process as it doesn’t require any energy from the cell since
substances move down their concentration gradient.
- Some of the substances transported in and out of cells by diffusion are oxygen and
carbon dioxide in gas exchange, and of the waste product urea from cells into the
blood plasma for excretion in the kidney.
- 3 factors affect the rate of diffusion:
Concentration gradient which is the difference in concentration between 2 places.
The larger the concentration gradient, the higher the rate of diffusion. More particles
are randomly moving down the gradient than are moving against it.
Higher temperatures give the particles more energy, so there are more successful
collisions per second and therefore a faster rate of diffusion. This means a higher
temp is a higher rate of diffusion.
Larger surface area means a higher rate of diffusion. The greater the surface area
the more space for particles to move through, faster rate of diffusion.
- Single-cells organisms use diffusion to transport molecules into the body from the air
because they have a large surface area to volume ratio. This means that diffusion
alone is enough to meet their needs.
- Multicellular organisms have a low surface area to volume ratio so they can’t rely on
diffusion alone so this means they have adaptations to help transport molecules in
and out of the cells.
- In the lungs oxygen is transported to the blood and carbon dioxide is transferred to
the lungs. This takes place across millions of alveoli which are covered with lots of
tiny capillaries that supply the blood.
- In the small intestine cells have villi. Digested food is absorbed over the membrane of
these cells and into the bloodstream.
- The gills are where gas exchange in fish takes place. Water which contains oxygen
passes through the mouth and over the gills. Each gill has gill filaments, upon these
gill lamellae where diffusion of oxygen in the blood and diffusion of carbon dioxide
into the water takes place. Blood flows in one direction while water flows in the other.
- The roots of plants are adapted to take up water and mineral ions. Roots have root
hair cells with large surface areas, which project into the soil.
, - In the leaves of the plant, carbon dioxide diffuses through the stomata for
photosynthesis, whilst oxygen and water vapour move out of them. The stomata are
controlled by guard cells which change the size of the stomata based on how much
water the plant received.
- Having a large surface area means more particles can move through resulting in a
faster rate of diffusion. For example cells of the small intestine have villi which
increases the surface area so that digested food can be absorbed into the blood
faster. The air spaces inside the leaf also increase surface area since it allows more
carbon dioxide to enter into the cell. In the lungs alveoli creates a very large surface
area. Fish gills contain lamellae to increase the surface area.
- A thin membrane provides a short diffusion pathway, allowing the process to occur
faster. For example in the lungs, alveoli and capillary walls are very thin and also villi
in the small intestine is very thin.
- Having an efficient blood supply creates a steep concentration gradient, so diffusion
occurs faster. For example the lungs constantly supply oxygen to make the blood
from alveoli capillaries oxygenated, by exchanging it for carbon dioxide that can be
breathed out. In fish, water also flows in one direction and blood flows in the other so
since the concentration of oxygen is much higher in the water - it will diffuse across
creating a steep concentration gradient.
Osmosis:
- Osmosis is the net movement of water molecules across a partially permeable
membrane, from a region of higher water concentration to a region of lower water
concentration.
- When a plant cell is placed in water, then water will move into the cell by osmosis
and the cell will expand. If we place the plant cell into a concentrated solution, then
water moves out of the plant cell by osmosis which causes the cell to shrink.
- If the external solution is more dilute, it will move into animal cells causing them to
burst.
- If the external solution is more concentrated, excess water will leave the cell causing
it to become shrivelled.
Active transport:
- The movement of molecules against the concentration gradient, so from a lower
concentration to a higher concentration.
- This requires energy from the cell and is an active process. This energy comes from
cellular respiration which happens in the mitochondria when they break down
glucose to release energy. The process is responsible for all energy that the cell
uses.
- Active transport always takes place across a membrane.
- Water molecules enter the root hair cell by osmosis
- Root hair cells are specialised to take up water by osmosis and mineral ions by
active transport from the soil. They have a large surface area for absorption of
mineral ions. Lots of mitochondria to provide energy for active transport of mineral
ions into the root hair cell.
Differentiation and Specialised cells:
- Cells may be specialised to carry out a particular function: sperm cells, nerve cells
and muscle cells in animals, root hair cells, xylem and phloem cells in plants.
- Sperm cells: the role is to deliver genetic information to an egg in order to fertilise it. It
has flagellum on the end which acts like a tail and allows the sperm cell to swim
