Flashcards in Basic Functions of Life- Processes Deck (17)
Cells are the smallest living things. Collections of cells working together make up multicellular life like us. Nothing smaller than a cell is alive. Many organisms are multicellular so the group of cells must ask collectively carry out all processes of life
Cells must get materials and energy from their environments. We call anything useful a cell acquires from outside a nutrient. (Anything harmful that a cell acquires is called a toxin.). Through this process, cells take in raw materials and energy to carry out all the work they must do.
All cells must release energy from food and use that energy to drive other processes. Some (autotrophs) can store energy sources that are not already in the form of organic food, such as sunlight. Respiration releases energy. Autotroughs provide energy for heterotrophs.
Cells use energy and nutrients to build the complex molecules that make up living tissue. Thus life is both a set of complex molecules and the factory for making those molecules. It is what biologists would call a “self-sustaining system”. The most important molecules that cells make are proteins called enzymes, which control all the other processes. Cells synthesize things like proteins, lipids, carbohydrates etc.
Cells are more organized than their environment, so what they get from the environment is never exactly what they need in their nutrients. They have some ability to neutralize or eliminate the things they don’t need, so they don’t become toxic.
Some molecules change in response to different stimuli, such as light or acid. To varying degrees, other life processes can be turned on or off, or accelerated and decelerated, in response to changes in the surrounding environment. The cell can change its own state. Some things in the cell are sensitive to the environment, others, like proteins, are able to change things in the cell. Response adjusts all other processes. Cells are so complex that they are unstable and will lose order if they are not maintained.
Most of the time, responses by cells reverse any changes caused by the environment and keep the state of a cell more stable than its environment. This stable state is called homeostasis. A cell must stay homeostatic within certain limits, or it will die. [Note that homeostasis is actually a condition or state, while other boxes in this flow chart are mainly processes that affect that condition.]
A homeostatic cell that stays alive and carries out more synthesis than it needs to maintain itself will grow. This means that it can grow its cytoplasm. Almost all cells have at least one period of growth. [Can you think of an exception?]
Cells must reproduce for two reasons. First, there is an upper limit to growth, before a cell stops functioning efficiently. Secondly, any cell will eventually die, even if only due to accident, so cells must produce copies as “insurance”. This is what we might call the “evolutionary imperative”. The only cells that continue to exist are those whose ancestors reproduced successfully, so all life is geared to reproduction. Reproduction= growth for multicellular organisms
What is life?
● carries out conversions of energy and matter – metabolism
● to maintain its own stability – homeostasis
● and ultimately to replicate itself (or its genes) – reproduction
Some people would also include evolution as a key character of life, on the basis that all life as we know it has been refined over time to be better at carrying out the three processes above.
4 ways of defining life
1) origins (mapping out life tree). 2) organization (do those organisms also have cells, tissues, organs etc.) 3) fundamental biochemistry (are they made up of the same stuff as us?) 4) fundamental processes (do they do the same activities of life as us?)
organism must have carbohydrates (provides structure + energy), lipids (energy, membranes), proteins (structure, controls other processes), nucleic acids (information)
example of response and homeostasis
we sweat to maintain body temp (37 degrees) which is response to when it is too hot.
All life is composed of cells and cell products.
The cell is the smallest living unit.
All cells come from pre-existing cells.
cell theory advantages
Ad+ It allows a simple, immediate, observable feature to separate almost all
life from everything else.
cell theory disadvantages
- does not include viruses which lack a cell
- does not allow origins of first cells from simple systems (most biologists agree that life came from complex chemical systems but that is not needed to understand evolution)