1.1 Introduction to cells Flashcards
The cell theory states that:
- Living organisms are composed of cells (one or more)
- Cells are the smallest units of life
- Cells come from pre-existing cells
Atypical cell: siriated muscle fibers
- Striated muscle tissue is composed of repeated units called sarcomeres
- Multinucleated
- About 30 mm long (larger than a typical cell)
Atypical cell: aseptate fungal hyphae
- This fungi is not partitioned by septa (dividing cell walls)
- Therefore there is a shared cytoplasm and multiple nuclei
Atypical cell: giant algae (Acetabularia)
- 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
Magnification
magnification = size of drawing/actual size
1000 nm (nanometres) = 1 μm (micrometre)
1000 μm (micrometres) = 1 mm (millimetre)
Unicellular organisms
- Organisms made up of one cell
- Hence they should be able to carry out all of the life processes within the cell
List the functions of life
Metabolism
Reproduction
Response
Homeostasis
Excretion
Nutrition
Growth
Metabolism
The life-supporting chemical reactions that take place within the cells of living organisms.
Reproduction
The production of offspring, either sexually or asexually, to pass on genetic information to the next generation.
Response (to a stimulus)
A reaction by the living organism to changes in the external environment.
Homeostasis
The maintenance of a stable internal environment by regulating internal cell conditions.
Excretion
The removal of waste products (from metabolism and other unimportant/toxicmaterials) from an organism.
Nutrition
The intake of nutrients.
- In plants: making organic molecules through photosynthesis
- In animals/fungi: the absorption of organic matter
Growth
An increase in size or shape that occurs over a period of time.
Paramecium (unicellular organism)
- 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
Chlamydomonas (unicellular organism)
- 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
SA:Vol
- 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
SA:Vol
Villi and microvilli
- 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
Multicellular organisms
- 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
Evolutionary steps to multicellular organisms:
- 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).
Organisation of multicellular organisms
Cells –> tissues –> organs –> organ systems –> organisms
Cell differentiation
- 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.
Stem cells
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
Totipotent stem cells
- 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)