1.1 Introduction to cells Flashcards
What is cell theory
- Living organisms are composed of cells
- Cells are the smallest unit of life
- All cells come from pre-existing cells
All cells contain
- All living cells are surrounded by a cell membrane
- All cells contain genetic information which controls function of the cell
- Cells generate energy to power activities of the cell
Exceptions to cell theory
- Skeletal muscle fibre: atypical as they are 1000x longer than normal cells and have many nuclei
- Fungal Hyphae: sometimes are not divided up into many cells, this creates one larger cell (septate or aseptate)
- Giant Algae: these cells are abnormally large compared to other algae cells. 1 nucleus and they can be up to 100mm long.
Organisms consisting of once cell carry out all the functions of life - and other facts
- nothing smaller than a cell can survive
- subcellular substances/organelles can live independent of the cell
What does MR GREHN stand for?
Metabolism Response Growth Reproduction Excretion Homeostasis Nutrition
Metabolism as a function of life
produce enzymes to control chemical reactions inside cell, including respiration
Response as a function of life
perceiving and responding to changes in the environment (stimuli)
Growth as a function of life
increase in size and dry mass
Reproduction as a function of life
producing offspring - sexually/asexually
Excretion as a function of life
Expel waste matter
Homeostasis as a function of life
keeping conditions within the organisms within tolerable limits
Nutrition as a function of life
obtaining food to provide energy and materials for growth
Metabolism in paramecium and chlamydomonas
Paramecium: produces enzymes to catalyse reactions within the cytoplasm
Chlammydomonas: same
Response in paramecium and chlamydomonas
Paramecium: reacts to stimuli - reverses its direction of movement when it touches a solid object
Chlamydomonas: reacts to stimuli - senses the brightest spot (using eye spot) and swims towards it
Growth in paramecium and chlamydomonas
Paramecium: increase in size + dry mass by accumulating organic matter and minerals from its food
Chlamydomonas: increase in size + dry mass by photosynthesising and absorption of minerals
Reproduction in paramecium and chlamydomonas
Paramecium: reproduces asexually by mitosis or sexually by meiosis and gametes
Chlamydomonas: same
Excretion in paramecium and chlamydomonas
Paramecium: expels waste products of metabolism (e.g. CO2 diffuses out)
Chlamydomonas: expels waste products of metabolism (e.g. O2 diffuses out)
Homeostasis in paramecium and chlamydomonas
Paramecium: maintains all internal conditions within limits (e.g. expels water using contractile vacuole)
Chlamydomonas: same
Nutrition in paramecium and chlamydomonas
Paramecium: Feeds on smaller organisms by ingesting and digesting them in vesicles (endocytosis)
Chlamydomonas: Produces its own food by photosynthesis using chloroplasts which take up much of the cell
SA : Vol ratio is important in the limitation of cell size
- In the cytoplasm of a cell many chemical reactions take place, these reactions are known as the metabolism of the cell.
- The rate at which chemical reactions can happen within a cell is proportionate to the volume of the cell.
- For metabolism to continue substances used in reactions must be absorbed by the cell and waste products removed.
- Substances move through the plasma membrane in and out of the cell.
- The rate at which substances can cross the membrane depend on its surface area.
Why a small SA : Vol ratio is bad
- If the surface area to volume ratio’ is too small then substances will not be able to enter the cell as quickly as they are required, and waste products will accumulate because they are produced more rapidly and can’t be excreted.
- If the surface to area ratio is too small then cells may overheat because metabolism produces heat faster that it is lost over the cells surface.
Multicellular organisms
- Many cells fused together to create a single mass of cells
- Cells are often specialised and together these cells create a functioning multicellular organism
- the cellular components of multicellular organisms are what allow them to function
Cell differentiation in multicellular organisms
- in multicellular organisms cells are specialised to perform different functions
- by becoming specialised, cells in a tissue can perform the function more efficiently than if they had many different roles
Gene expression and cell differentiation
- all cells in the human body have the same amount of genes however certain cells only express certain genes so that they can perform their function
- example of differentiation: skin cells inside the human nose all express different genes so that they can pickup different smells
Two important factors of stem cells
- stem cells can divide many times to produce large amounts of new cells
- stem cells are not fully differentiated; they can differentiate into different cell types
Stem cells and medicine (therapeutic treatments)
stem cells can be very useful for medical applications, they can produce regenerated tissue, and possibly in the future produce whole new hearts and kindneys. these are therapeutic treatments
- also used for stargarts macular dystrophy
- leukemia
other applications of stem cells (food)
stem cells can be used to produce large quantities of striated muscle fibres, or meat for human consumption.
Where stem cells are found
in adults: bone marrow, skin and liver.
these allow for regeneration and repair.
-stem cells in other tissues only allow for limited repair; brain, kidney and heart.
Advantages of Large SA:Vol ratio
- diffusion pathways are shorter, so more efficient
- molecules do not have to travel as far to get in and out of the cell, therefore it takes less time and (if active transport) energy.
- concentration gradients are easier to generate (efficient diffusion)
Disadvantages of Large SA:Vol ratio
-warm blooded mammals lose heat very quickly due to the large SA:Vol ratio
Four facts about SA:Vol ratio
- cells divide so SA:Vol ratio doesn’t get too small
- the rate of metabolism of a cell is a function of its mass/volume
- the rate of material exhange in and out of a cell is a function of its surface area
- as the cell grows volume increases faster than surface area (so less SA:Vol ratio)
Emergant Properties
Emergant properties arise from the interaction of component parts. The whole is greater than the sum of its parts. Multicellular organisms are capable of completing functions that individual cells could not undertake - this is due to the interactions between cells producing new functions.
Mechanisms other than cell division used to maintain a viable SA:Vol ratio in multicellular organisms
- Compartmentalisation (alvedi)
- Change surface (root hairs)
- Change shape
Ethics of stem cell use
some people say an embryo is a human whereas other say that because there is no nervous system it is nothing more than a few cells
Stargardts Disease
-Downsides or ethical issues
Downsides / Ethical issues: there are no harmful side effects
-ethical issues involve the harvesting of embryonic stem cells and the controversy surrounding embryonic stem cell use
Leukemia
-downsides or ethical issues
Downsides / Ethical issues: common side effects of stem cell therapy include: nausea, vomiting, fatigue and temporary hair loss
- ethical issues involve the harvesting of embryonic stem cells and the controversy surrounding embryonic stem cell use
Classes of stem cells
totipotent, multipotent, pluripotent
Pluripotent stem cells
later embryonic stem cells, (differentiation) all cell types that make up the human body
Multipotent stem cells
adult stem cells + cord blood stem cells (differentiation) more than one cell type (limited)
Totipotent stem cells
early embryonic stem cells, within the first couple of cell divisions (differentiation) all cells + placental cells
Specialised tissues
these can develop by cell differentiation in multicellular organisms
Tissue
- a group of differentiated cells
- as a result the cell group can carry out specialised functions that other tissues may not be able to
Stargardts disease Cause
Cause: Caused by a recessive mutation of a gene called ABCA4
-This causes a membrane protein used for active transport in retina cells to malfunction
Stargardts disease symptoms
Symptoms: photoreceptive cells in the retina degenerate
- vision becomes progressively worse
- can lead to blindness
Stargardts disease treatment
Treatment: embryonic stem cells are developed into retina cells
- retina cells derived from embryonic stem cells are injected into patient’s eye (approx. 50,000)
- the cells attach to the retina and remain there
- this results in the improvement in vision
Leukaemia cause
Cause: caused by a mutation in genes that control cell division
- several specific mutations occur in one cell
- cancer-inducing mutations in a cell cause it to grow and divide repeatedly
- Leukemia involves the production of abnormally large numbers of white blood cells
Leukaemia symptoms
Symptoms: -an enormous increase in white blood cell count
- destroys the immune system
- makes you susceptible to death by the common cold or simply bleeding out if you have a small cut
- bone pain, skin rashes, headaches, vision problems, chest pains
Leukaemia treatment
Treatment: fluid is removed from the bone marrow
- stem cells are extracted from the fluid and frozen
- chemotherapy drugs are administered, they kill all cancer cells in bone marrow, bone marrow loses ability to produce red blood cells
- frozen stem cells are returned to the patient’s body and start the production of red and white blood cells
