Topic 1 - Cell biology

Eukaryotic cells

-have genetic material that forms chromosomes and is contained in the nucleus

-much bigger than prokaryotic cells

-plant and animal cells

Subcellular structures

-cell membrane which controls the movement of substances in and out of the cell

-nucleus which contains DNA

-mitochondria which is where energy is released through respiration

-cytoplasm which is where chemical reactions take place

-permanent vacuole which stores cell sap

-chloroplasts which contain chloroplasts that absorb light energy for photosynthesis

-cell wall which is made of glucose to strengthen the cell wall

Animal cell subcellular substructures

-cell membrane

-nucleus

-mitochondria

-ribosomes

-cytoplasm

Plant cell subcellular structure

-cell membrane

-nucleus

-mitochondria

-ribosomes

-cytoplasm

-permanent vacuole

-chloroplasts

-cell wall

Prokaryotic cells

-single celled

-no nucleus and have a single loop of DNA

-have small rings of DNA called plasmids

-smaller than eukaryotic cells

-bacteria

Subcellular structures in prokaryotic cells

-cell wall

-cytoplasm

-cell membrane

-flagellum

-bacterial DNA loop

-plasmid DNA rings

Light microscopes

-use light to form images

-living samples can be viewed

-relatively cheap

-low magnification

-low resolution

-can't see sub cellular structures

Electron microscopes

-uses beams of electrons to form images

-sample cannot be living

-expensive

-high magnification

-high resolution

-allow you to view sub cellular structures

Magnification equation

-image size/object size

Specialised cells

-cells in plants in animals and plants that differentiate to form types of cells that are adapted to perform a particular function

Sperm cell adaptation

-tail to swim to the ovum and fertilise it

-lots of mitochondria to release energy from respiration which enables the sperm to swim to the ovum

Red blood cell adaptation

-no nucleus so more room to carry oxygen

-contains a red pigment called haemoglobin to bind to oxygen molecules

-flt biconcave shape to increase surface area to volume ratio

Muscle cell adaptation

-contains protein fibres which can contract to make the cell shorter

-contains lots of mitochondria to release energy from respiration allowing the muscle to contract

Nerve cell adaptation

-branched endings called dendrites to make connections with other neurones and effectors

-myelin sheath which insulates the axon in order to increase the transmission speed of electrical impulses

Palisade cell adaptations

-lots of chloroplasts containing chlorophyll to absorb light energy for photosynthesis

-located at the top surface of the leaf where it can absorb the most light energy

Diffusion

-the spreading out of particles resulting in a net movement from an area of high concentration to a low concentration

-particles move down the concentration gradient from an area of high concentration to a low concentration

-passive process meaning no energy is required

Diffusion in humans

-nutrients in the small intestine diffuse into the capillaries through the villi

-oxygen diffuses from the air in the alveoli into the blood in the capillaries and carbon dioxide diffuses from the blood in the capillaries into the air in the alveoli

-urea diffuses from cells into the blood or excretion in the kidney

Diffusion in fish

-oxygen from water passing over the gills diffuse into the blood in the gill filaments

-carbon dioxide diffuses from the blood in the gill filaments into the water

Diffusion in plants

-carbon dioxide used for photosynthesis diffuses into leaves through the stomata

-oxygen produced during photosynthesis diffuses out of the leaves through the stomata

Osmosis

-the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane

-water moves from an area of lower solute concentration to an area of higher solute concentration

-passive process meaning no energy is requited

Osmosis in plants

-water moves by osmosis from a dilute solution in the soil to a concentrated solution in the root hair cell

Active transport

-particles move against the concentration gradient meaning they move from an area of low concentration to an area of high concentration

-not a passive process meaning energy is required

Active transport in humans

-active transport allows sugar molecules to be absorbed from the small intestine when the sugar concentration is higher in the blood than in the small intestine

Active transport in plants

-used to absorb mineral ions into the root hair cells from more dilute solutions in the soil

Factors that affect the rate of diffusion

-the steeper the concentration gradient, the faster the rate of diffusion

-the higher the temperature, the faster the rate of diffusion

-the larger the membrane surface area, the faster the rate of diffusion

Adaptation of villi in the small intestine for absorbing nutrients

-network of capillaries

-large surface area to volume ratio to ensure enough molecules can be transported across the cell membranes to meet the needs

-thin wall which is only cell thick allowing a short diffusion path

-good blood supply

Adaptations of the alveoli in the lungs for gas exchange

-network of capillaries which provide a good blood supply

-the membrane in the alveoli has a large surface area and is one cell thick increasing the rate of diffusion and proving a short pathway for diffusion

Adaptations of fish gills for gas exchange

-made with stacks of thin filaments which have a large surface area and a network of capillaries providing a good blood supply that help increase the rate of diffusion

Adaptations of root hair cells for uptake of water and minerals

-lots of mitochondria for lots of energy to be released from respiration for active transport of mineral ions

-large surface area providing efficient absorption of water and minerals

The cell cycle

-body cells divide to form two identical daughter cells by going through a series of stages

-cell division by mitosis is important for growth and repair of cells

-mitosis is also used for asexual production

Stage 1 of the cell cycle

-cells grow bigger

-DNA replicates meaning chromosomes are duplicated

-increased number of subcellular structures such as ribosomes and mitochondria

Stage 2 of the cell cycle

-a complete set of chromosomes is pulled to each end of the cell

-the nucleus divides to form two nuclei

Stage 3 of the cell cycle

-cytoplasm and cell membrane divide to form two identical daughter cells

Stem cells in medicine

-a stem cell is an undifferentiated cell that can develop into one or more types of specialised cell

-the two types of stem cells in animals are adult stem cells and embryonic stem cells

-the stem cells in plants are plant meristem

-stem cells can be cloned to produce large numbers of identical cells

Adult stem cells

-found in specific parts of the body in adults and children such as bone marrow

-can only differentiate to form certain types of cells for example stem cells in bone marrow can only differentiate to form blood cells

Advantages of adult stem cells

-fewer ethical issues as adults can consent to have their stem cells removed and used

-established technique for treating diseases such as leukaemia

-relatively safe to use as treatment and donors recover quickly

Disadvantages of adult stem cells

-requires a donor potentially causing a long waiting time to find someone suitable

-can only differentiate into certain types of specialised cells so fewer disease can be treated

Embryonic stem cells

-found in early human embryos

-can differentiate into any type of specialised cell in the body

Advantages of embryonic stem cells

-can treat a wide range of diseases as they can differentiate into any type of specialised cell

-may be possible to grow whole replacement organs

-usually no donor is needed as they are obtained from spare embryos from fertility clinics

Disadvantages of embryonic stem cells

-ethical issues as the embryo is destroyed and each embryo is a potential human life

-risk of transferring viral infections to the patient

-newer treatment so it is relatively under researched meaning it is not yet clear if they can cure as many diseases as thought

Plant meristem

-found in meristem regions in the roots and shoots of plants

-can differentiate into any type of cell and can be used to create whole clones of plants

Advantages of plant meristem

-rare species of plants can be cloned to prevent extinction

-plants with desirable characteristics such as disease resistance can be cloned t produce large numbers of identical plants

-fast and low cost production of a large number of plants

Disadvantages of plant meristem

-cloned plants are genetically identical so a whole crop is at risk of being destroyed by a single disease or genetic defect

Therapeutic cloning

-cells from a patient's body are used to create a cloned early embryo of themselves

-stem cells from this embryo can be used for medical treatments and growing new organs

-these stem cells have the same genes as the patient so they are less likely to be rejected when transplanted