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Biology SL > 1.1 Introduction to cells > Flashcards

1.1 Introduction to cells Flashcards

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1
Q

The cell theory states that:

A
  1. Living organisms are composed of cells (one or more)
  2. Cells are the smallest units of life
  3. Cells come from pre-existing cells
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2
Q

Atypical cell: siriated muscle fibers

A
  • Striated muscle tissue is composed of repeated units called sarcomeres
  • Multinucleated
  • About 30 mm long (larger than a typical cell)
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3
Q

Atypical cell: aseptate fungal hyphae

A
  • This fungi is not partitioned by septa (dividing cell walls)
  • Therefore there is a shared cytoplasm and multiple nuclei
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4
Q

Atypical cell: giant algae (Acetabularia)

A
  • Very large in size (ranges from 0.5-10 cm)
  • Challenges the idea that cells are small in size and that larger organisms are always made of many microscopic cells
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5
Q

Magnification

A

magnification = size of drawing/actual size
1000 nm (nanometres) = 1 μm (micrometre)
1000 μm (micrometres) = 1 mm (millimetre)

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6
Q

Unicellular organisms

A
  • Organisms made up of one cell
  • Hence they should be able to carry out all of the life processes within the cell
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7
Q

List the functions of life

A

Metabolism
Reproduction
Response
Homeostasis
Excretion
Nutrition
Growth

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8
Q

Metabolism

A

The life-supporting chemical reactions that take place within the cells of living organisms.

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9
Q

Reproduction

A

The production of offspring, either sexually or asexually, to pass on genetic information to the next generation.

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10
Q

Response (to a stimulus)

A

A reaction by the living organism to changes in the external environment.

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11
Q

Homeostasis

A

The maintenance of a stable internal environment by regulating internal cell conditions.

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12
Q

Excretion

A

The removal of waste products (from metabolism and other unimportant/toxicmaterials) from an organism.

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13
Q

Nutrition

A

The intake of nutrients.
- In plants: making organic molecules through photosynthesis
- In animals/fungi: the absorption of organic matter

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14
Q

Growth

A

An increase in size or shape that occurs over a period of time.

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15
Q

Paramecium (unicellular organism)

A
  • Paramecium is a genus (group) of unicellular protozoa
  • Responsiveness: They are covered by cilia (small hair-like structures), allowing them to move
  • Nutrition: they are heterotrophs (feeds of food particles they encounter in their environment).
  • Metabolism: food particles are enclosed within small vacuoles that contain enzymes for digestion
  • Homeostasis: osmoregulation (helps maintain their water balance by collecting excess water in the contractile vesicles and expelling it through the plasma membrane). Gases enter (O2) and exit (CO2) via cell diffusion
    Reproduction: it can carry out both sexual and asexual reproduction, the latter is more common –> the cell divides into two daughter cells in a process called binary fission.
    Excretion: wastes removed via the anal pore
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16
Q

Chlamydomonas (unicellular organism)

A
  • A genus of unicellular green algae (Chlorophyta)
  • They have a cell wall, a chloroplast, an ‘eye’ that detects light, as well as two flagella (used to swim)
  • Nutrition: they are autotrophs (they make their own food using their large chloroplast to photosynthesize).
  • Response: It senses light changes with its ‘eye’ and uses the flagella to move towards it to increase the rate of photosynthesis.
  • Homeostasis: osmoregulation (helps maintain their water balance by collecting excess water in the contractile vesicles and expelling it through the plasma membrane).
  • Reproduction: when the organism reaches a certain size, each cell reproduces, either by binary fission (asexual) or sexual reproduction.
  • Excretion: uses the whole surface of it’s plasma membrane to excrete it’s waste products
17
Q

SA:Vol

A
  • As a cell grows, volume increases faster than surface area, leading to a decreased SA:Vol ratio
  • To survive, a cell needs to import molecules and expel waste products through its plasma membrane.
  • If a cell’s surface area is too small compared to its volume, not enough of the necessary molecules can get in and not enough waste (including heat) can get out.
  • Suitable: HIGH SA to Vol ratio
18
Q

SA:Vol
Villi and microvilli

A
  • Cells and tissues that are specialised for gas or material exchanges will increase their surface area to optimise material transfer
  • Villi: small folds that increase the SA, found in the small intestine (exposed to digested food to absorb nutrients).
  • Microvilli: small folds on the cell membrane of villi which increase the SA even more, allowing nutrients to be absorbed more efficiently
19
Q

Multicellular organisms

A
  • Organisms composed of more than one cell, with groups of cells differentiating to take on specialized functions.
  • Have properties that emerge from the interaction of their cellular components
20
Q

Evolutionary steps to multicellular organisms:

A
  • Life on this planet probably started out as small unicellular organisms.
  • Some of these cells clumped together and over long periods of time began to work together, evolving into simple multicellular organisms.
  • Organisms grew larger because they were no longer limited by the size of one cell.
  • Cells in such an organism were able to specialise through differentiation (unspecialized cells –> specialized cells, distinct structure and function).
21
Q

Organisation of multicellular organisms

A

Cells –> tissues –> organs –> organ systems –> organisms

22
Q

Cell differentiation

A
  • All cells of an organism share an identical genome – each cell contains the entire set of genetic instructions for that organism
  • Not all genes are activated in every cell
  • By activating certain genes and not others, the cells are able to differentiate.

Emergent properties:
- According to emergent properties, a complex system possesses properties that its constituent parts do not have.
- The whole is more than the sum of its parts.

23
Q

Stem cells

A

A stem cell is an undifferentiated/unspecialized cell that:
1. form more cells of the same type indefinitely
2. can differentiate into specialized cells

  • However, not all stem cells can give rise to all body cells. There are 4 different types of stem cells: totipotent, pluripotent, multipotent, unipotent
24
Q

Totipotent stem cells

A
  • Can differentiate into any type of cell, including placental cells
  • Can give rise to a complete organism
  • Example: the eight cells of the morula (the first cells formed following fertilisation of an egg cell)
25
Q

Pluripotent stem cells

A
  • Can differentiate into all body cells
  • But cannot give rise to a whole organism
  • Example: embryonic stem cells of the blastocyst
26
Q

Multipotent stem cells

A
  • Can differentiate into a few closely related types of body cell.
  • Example: umbilical cord stem cells
27
Q

Unipotent stem cells

A
  • Can only differentiate into their associated cell type
  • Meaning they are capable of self renewal
  • Example: liver stem cells (can only make liver cells)
28
Q

Uses of stem cells

A

Stem cells are a viable therapeutic option when cells/tissues that are not capable of self-renewal (non-stem cells) become damaged
Examples:
- Treatment of Parkinson’s disease
- Treatment of leukemia
- Growth of transplant organs

29
Q

Use of stem cells to treat diseases: Stargardt’s disease

A
  • A disease of the eye
  • An inherited form of juvenile macular degeneration (affects a small area near the centre of the retina) that causes progressive loss of central vision
  • Typically appears in late childhood to early adulthood
  • Caused by a recessive gene mutation that makes the photoreceptor cells degenerate
  • Patients are injected retinal cells derived from human embryonic stem cells into the retina
  • The inserted cells attach to the retina and become functional
30
Q

Use of stem cells to treat diseases: leukemia

A
  • A type of cancer of the blood or bone marrow caused by high levels of abnormal white blood cells
  • People with leukemia have a higher risk of developing infections, anemia and bleeding
  • The treatment involves harvesting hematopoietic stem cells (HSCs), which are multipotent stem cells
  • HSCs can be taken from bone marrow, peripheral blood or umbilical cord blood (from either the patient or a suitable donor)
  • The patient undergoes chemotherapy and radiotherapy to get rid of the diseased white blood cells and then HSC’s are transplanted back into the bone marrow to differentiate into new healthy white blood cells
31
Q

Stem cells can be derived from:

A
  • Embryos (may be specially created by therapeutic cloning)
    *Requires the destruction of a potential living organism
  • Umbilical cord blood or placenta of a new-born baby
    *Easy to collect, no risk for the mother or the baby
    *Issues of availability and access (they have to be stored and preserved at cost)
  • Certain adult tissues like the bone marrow (cells are not pluripotent)
    *Limited in the scope of application
32
Q

Ethical issues of using stem cells (embryos: destruction of potential life)

A
  • Of the different sources of stem cells, harvesting from embryos is the most controversial
    Arguments supporting:
  • Cells may be used in therapies to eliminate serious diseases or disabilities in the human population
  • Transplants can be easily obtained without requiring the death of another human or inflicting any kind of pressure on a normal functioning body which happens when someone donates an organ
  • The stem cells are harvested from an embryo at such an early state where it has not yet developed a nervous system and thus it’s likely to not feel any pain.
33
Q

How embryos are created to produce stem cells

A
  1. Removal of nucleus from donor egg
  2. Host DNA (from somatic cells) is transfered into the nucleus of the donor egg
  3. When the egg becomes a blastocyst the stem cells are harvested
34
Q

Reasons for the therapuetic use of stem cells

A
  • Unspecialized stem cells can differentiate along different pathways
  • They are accessible as they come from embryos/bone marrow/umbilical cord/adult tissue
  • Stem cells can regenerate damaged/diseased tissues in people

Biology SL (37 decks)

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