Basic structure
Bacteria are unicellular organisms that are found in so many places - we don't actually realize the extent to which they live. There thousands found inside and on us!
Bacteria all contain some DNA however it is not found within a nucleus - it just floats around the cytoplasm. Bacteria have both a cell wall and a cell membrane. They also have a slime capsule which offers them protection. Bacteria have one main organelle, ribosomes, which produce proteins (needed to make enzymes and have many other functions). They may also contain aflagella (tail). They are incredibly small and can only be seen under a microscope, unless grown in colonies on an agar plate - which we can see because there are so many. |
Helpful vs. harmful bacteria
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LIFE PROCESSES
N E R R G
Nutrition
Bacteria can be autotrophic or heterotrophic.
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Autotroph
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Heterotroph
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Some species of bacteria can actually make their own food, just like plants! These types of bacteria can be referred to as autotrophic, or autotrophs.
Many bacteria are heterotrophs - they can only gain nutrients from eating and digesting other organic (living, was once living) material. If bacteria gain their nutrients from dead or decaying matter, they are called saprotrophs. Other bacteria can gain nutrients from eating living organisms - they are just called heterotrophs.
Parasitism
When a bacterium lives and feeds off living matter, causing harm to that organism, the bacterium is called a 'parasite'.
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Mutualism
Some bacterium have a relationship with their host where they both benefit (e.g. bacterium inside the gut of herbivores) - these bacteria are called mutualists.
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Commensalism
Bacteria that do neither harm nor good to their host are called commensals - for example bacteria that live on our skin.
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Heterotrophic bacteria must break down (digest) the organic matter of other organisms.
They do this using a process called extra-cellular digestion.
They do this using a process called extra-cellular digestion.
There are 3 steps to this process:
1. Enzymes are made and secreted (released) onto the food source.
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2. The enzymes break down the organic matter by speeding up the catabolic ("breaking-down") reactions that must occur.
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3. The enzymes and digested nutrients are absorbed back into the bacterial cell via active transport.
Note: active transport is the bulk-movement of substances across a semi-permeable membrane, requiring energy |
STARCH IS CONVERTED TO GLUCOSE |
PROTEINS ARE CONVERTED TO AMINO ACIDS |
FATS ARE CONVERTED TO FATTY ACIDS AND GLYCEROL |
Glucose is then broken down to release energy (this is the process of respiration). |
Amino acids are used to build more enzymes and proteins that the bacteria needs. |
Fatty acids and glycerol are used to make new parts of the cell and to support bacterial growth. |
Food (such as starch, a carb) must be broken down to be used by the bacterium. In its original form, the substance is too large to be used as required. Starch cannot be used for respiration, only glucose. Therefore larger food molecules must be broken down into their smaller counterparts in order to be used up.
- For example, our cells cannot use potatoes in potato form, they need to be chewed up, broken down by the acids in our stomach (into their simplest form - glucose) and only THEN can they be used by our cells for energy.
Excretion
Bacteria need to get rid of their waste, too.
All cells produce waste products - it is all a part of 'living' - when cells undergo respiration (below) they make products they use, and waste products that need to be discarded. When our cells undergo respiration, they take in oxygen and release carbon dioxide. Carbon dioxide is a waste product which we excrete by breathing out.
Bacteria excrete their waste from the cytoplasm. The waste travels from there, through the cell membrane, cell wall and eventually reaches outside of the cell where it is left. Waste can affect organisms nearby, as in a way, it contaminates the bacterium's surroundings. Waste can have different effects:
Bacteria excrete their waste from the cytoplasm. The waste travels from there, through the cell membrane, cell wall and eventually reaches outside of the cell where it is left. Waste can affect organisms nearby, as in a way, it contaminates the bacterium's surroundings. Waste can have different effects:
Harmful waste |
Smelly waste |
Helpful waste |
When bacterial waste accumulates, it can become toxic. When this happens, the waste is referred to as toxins. Toxins can kill neighbouring cells, including other bacteria! If the amount of toxins gets too great, the bacteria producing all the waste could die too! |
Bacteria that feed on our sweat produce a smelly waste, which is why we stink after exercising! Particularly our armpits and feet! Yuck! |
The waste products made by bacteria can be very handy for us and other organisms. For example, bacteria found in the soil can excrete nitrates and plants use this as food! The bacteria we use to make yoghurt creates an acidic waste product when it does respiration. Because of its acidity, the waste is able to change the pH of the yoghurt mixer and this actually gives us thick yoghurt! Yum! |
Respiration
Making useable energy using enzymes.
When oxygen is available, bacteria will undergo aerobic respiration.
Aerobic respiration is far more efficient (makes more energy) than anaerobic - so whenever there's oxygen around, bacteria will default to this type.
The equation for aerobic respiration is: Glucose + Oxygen → ATP + Carbon dioxide + Water
(carbon dioxide and water are waste products - must be excreted) |
When oxygen is unavailable, bacteria will undergo anaerobic respiration.
Some bacteria live in places where there's no oxygen available, such as in mud! In these cases, bacteria will undergo anaerobic respiration to produce energy.
Glucose → ATP + Lactic acid
This process is also called fermentation. (lactic acid is a waste product - must be excreted - is what helps make yoghurt clumpy) |
Growth
Bacteria must grow before they can reproduce.
In preparation for reproduction, bacterial cells absorb as much water and nutrients as possible, and use the nutrients they absorb to make new structures. These structures might include membranes and DNA. When bacteria become about twice their original size, they can then reproduce. Bacterial cells cannot become too large in size, as it would take too long for necessary molecules to reach the required location in the cell for particular processes to occur - due to the cell's large diameter!
Population growth
If conditions are perfect for growth AND reproduction, one bacteria can reproduce once every 20 minutes. In one hour, if you started off with one bacterium, you would end up with 8. Imagine if you started off with 1000 bacteria! This type of fast-growth is called exponential growth, because each time reproduction occurs, the entire population doubles in size.
When population numbers get high, some problems start to appear. For example, all the food will get used up. Toxins are likely to accumulate due to ALL the bacteria excreting their waste. The population will eventually reach a point where some members will die off.
When population numbers get high, some problems start to appear. For example, all the food will get used up. Toxins are likely to accumulate due to ALL the bacteria excreting their waste. The population will eventually reach a point where some members will die off.
Reproduction
Bacteria reproduce using a process called binary fission.
Think about it...
Why do we put food in the fridge to make it last longer?
How does refrigerating food affect baterial life processes?
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