Once massive stars reach the red giant phase, the core temperature continues to increase as carbon atoms are formed from the fusion of helium atoms. Gravity continues to pull together the carbon atoms in the core until the temperature reaches 600,000,000 degrees Celsius. At this temperature, carbon atoms form heavy elements such as oxygen and nitrogen. The fusion and production of heavy elements continues until iron starts to form. At this point, fusion stops and the iron atoms start to absorb energy. This energy is eventually released in a powerful explosion called a supernova. A supernova can light the sky up for weeks. The temperature in a supernova can reach 1,000,000,000 degrees Celsius. This high temperature can lead to the production of new elements which may appear in the new nebula that results after the supernova explosion. The core of a massive star that is 1.5 to 4 times as massive as our Sun ends up as a neutron star after the supernova. Neutron stars spin rapidly giving off radio waves. If the radio waves appear to be emitted in pulses (due to the star's spin), these neutron stars are called pulsars. The core of a massive star that has 10 or more times the mass of our Sun remains massive after the supernova. No nuclear fusion is taking place to support the core, so it is swallowed by its own gravity. It has now become a black hole which readily swallows any matter and energy that comes too near it. Some black holes have companion stars whose gases they pull off. As the gases are pulled down into the black hole, they heat up and give off energy in the form of X-rays. Black holes are detected by the X-rays which are given off as matter falls down into the hole.
In simple terms, Cell Theory can be expressed as living organisms are composed and consists of cells and it arises from the surviving cells (existing cells).
<u>Explanation:</u>
Cell Theory:
- The term "Cell Theory" has created an impact in the biology field and it is now confirmed that cell provides the basic structure to the living organisms and Robert Hooke started doing researching about the cells.
Principles of cell theory:
The three principles to the cell theory are listed here,
- All organisms are made up of one or more cells.
- Cells arise from other cells.
- The Cell is the fundamental unit of structure and organization.
Contribution to Cell Theory:
- Schwann and Schleiden are the two scientists who discovered lots of information about the cells and they have contributed lots to cell theory.
- Schleiden states that every part of plants are consists of cells and he states that cells were done by the crystallization process.
- Schwann states that every part of plants and animals were consists of cells.
- Based on their contribution postulates of cell theory has been proposed.
<u>Types of cells:</u>
The cells are classified as Eukaryotes Cell and Prokaryotes Cell
- Presence of Mitochondria
- Presence of Cytoskeleton
- Presence of Membrane-bound Nucleus
Examples: Animals and plants
- Absence of Mitochondria
- Absence of Cytoskeleton
- Absence of Membrane-bound Nucleus
Examples: Bacteria
A forest fire causes a dramatic, sudden reductions in population size. It affects all population in this way, regardless of whether they are big or small.