After an entire round of apologizing and attempting to figure out how to go about teaching you science, I think I’ve mostly got it figured out.
I almost gave up on this blog, I felt so certain that it was a waste of time and it wasn’t helping anyone, but people have sent me emails telling me how much I’ve helped them and I just want to say that I am SO grateful to all of you, and I’m so so happy that I’ve been able to help.
As another note, most of my emails have been deleted thanks to a certain 4 year old, and I emptied my trashcan before realizing it. I had a lot of emails that I hadn’t read or answered to yet so if you see this message and know that you’ve recently sent me an email that I haven’t responded to yet, please resend it, thank you!
I’m only briefing on science, I will not go into tons of detail but just enough for you to pass, however if you need help understanding any certain bit, email me at firstname.lastname@example.org and I will do my absolute best to help you.
If there is anything in this section you don’t understand, send me a message (anon or not) and I’ll try better to explain it.
Most of this knowledge comes straight from GED Success 2004, as always. So credit goes to Thompson Peterson’s.
Without further ado, Life Science - Cells.
There are two types of cells, the Prokaryotic cells and the Eukaryotic cells.
The difference between the two is that the Pro’s don’t have a true nucleus, whereas the Eukaryotic cells do.
Prokaryotes are mostly microscopic and only one-celled.
Prokaryotes include mostly bacteria and Archaea (microscopic, single celled organisms that live in extreme environments).
Eukaryotes are cells that have a true nucleus and well defined organells (or subcellular chemical structures). They may exist as single cells or as multicellular organisms.
Eukaryotes are the type of cells that make up plants and animals.
Every single eukaryotic cell (and most, if not all prokaryotic) has a cell membrane, and this membrane is what separates the cell itself from the outside world. They’re composed of very tightly packed fat, protein and carbohydrate molecules. They do have some openings called pores that go to the outside of the cell.
Within the membrane is the cytoplasm, it surrounds the nucleus, and it is a rather jelly-like substance. The cytoplasm is what houses the organelles.
The nucleus is the organelle that contains chromosomes, it also controls the cell’s growth and reproduction, as well as the cell’s metabolism.
The Endoplasmic Reticulum (ER) is also found in the cytoplasm. It’s an intricate canal system of sorts, and it assists in producing, manufacturing or digesting large chemical molecules. The ER may contain other organelles called ribosomes, which make protein.
Chloroplasts will only be found in plant cells, and they convert light energy into chemical energy (photosynthesis).
Mitochondria (which can be found in both animal and plant cells), take sugar molecules made in photosynthesis and transfer the chemical energy to a high-energy molecule called ATP, which the cells can readily use. The process that Mitochondria uses is called Respiration.
The cytoskeleton gives the cell its shape, it functions along with the centrioles (which are found in animal cells and work in conjunction with cilia and flagella -tiny hairlike growths- to allow the cell to move).
Also found in the cytoplasm are membranous sacs that transport materials in, within, and out of the cell.
The Cell Membrane:
The cell membrane is like a giant wall, it surrounds and protects the rest of the cell and the nucleus. It controls what enters and leaves the cell, and its composed of fat and oil (phosphate/lipid) molecules which are packed together.
Throughout the cell membrane are large protein molecules and carbohydrate chains, and they’re used as identifiers/markers by the cell and external molecules.
Some proteins act as pores in the membrane so that some materials may pass directly into the cell. Molecules may leave or enter the cells by chemical diffusion, osmosis or active transport (which requires energy).
Cell Functions are chemical reactions that use the food we eat to provide energy and raw materials for the cell’s use.
As food is composed of chemicals, our cells break down the food and use the molecules from it to make the molecules the cell needs to survive.
All metabolic activity (cellular metabolic reactions) is made possible by the action of Enzymes (protein molecules needed in very small amounts to bring about a chemical reaction).
Cells store the information about how to make the proteins its composed of in the DNA which is housed in the cell nucleus.
Small segments of DNA (called genes) direct the making of numerous specific proteins needed by the cell.
DNA also regulates which genes are active and which proteins are made. DNA regulation allows cells to relate to their environments, it also governs the growth of cells and their division.
Plants and animals grow from one original cell that divides by a highly regulated process called Mitosis.
Mitosis is a type of cell division that is necessary for growth of an organism and for the repair of damaged tissues or organs. The process of mitosis begins with one cell, which divides into two cells (which both have the same number and kind of chromosomes as the original cell), it’s a continuous process which scientists have divided into 4 phases in order to make it simpler to study.
1: Prophase - The nuclear membrane disappears, and the chromosomes become distinct, and a spindle appears. (Spindle is a cellular structure that organizes and separates the chromosomes during cell division)
2: Metaphase - the duplicated chromosomes are lined up on the equator of the cell
3: Anaphase - The duplicated chromosomes split apart and travel to the opposite poles of the cell.
4: Telophase - A nuclear membrane develops around the chromosomes at each pole, and the chromosomes become indistinct. During this phase, the division of the cytoplasm (called cytokinesis) is completed. There are now two smaller cells in the space of the original cell.
At the very beginning, before Prophase starts, imagine a ball, with just a bit of string in it. That string is the indistinct chromosomes.
As interphase begins, the string begins to be cut into pieces, each of those pieces has a perfect duplicate. That means a perfect match for every chromosome.
During metaphase, those chromosomes line up in the center of that little ball.
During Anaphase, the chromosomes divide up into two groups, one from the perfectly duplicated chromosomes go to one end, and the other chromosome goes to the opposite end, and those chromosomes sort of pull in the opposite directions. One side pulls the cell to the left, one side pulls it to the right, and it splits apart.
Leaving you with telophase and cytokinesis.
Those two cells start to grow and develop (called the Interphase) then they begin Mitosis all over again.
That isn’t exactly how it happens obviously, but perhaps it can give you a good mental image of how it works.
The Cell Cycle: