Tutor profile: Xenia R.
Subject: Environmental Science
What are the different trophic levels?
There are five trophic levels. We can think of them as a "pyramid", with primary producers as the widest section on the bottom and tertiary consumers as the smallest section on the top. Decomposers scale the sides of the pyramid. The higher up the pyramid we go, the less biomass (amount of organisms in a given area) there is. The first trophic level consists of the primary producers, which include plants, algae, and certain bacteria. Organisms use photosynthesis to convert the abiotic energy from sunlight into organic compounds which other organisms can use. For example, grass. The second trophic level is the primary consumers, which is made up of herbivores. These are animals that eat primary producers. For example, mice. The third trophic level is the secondary consumers, which consists of carnivores and omnivores. Carnivores are animals that eat herbivores. Omnivores eat both primary producers and herbivores. For example, a snakes (carnivores) or bears (omnivores). The fourth trophic level is the tertiary consumers, also known as the "top" predators. These are animals that eat other carnivores and omnivores. For example, hawks. The final trophic level is the decomposers. These organisms break down dead organic matter. They create a link from higher trophic levels down to lower ones. For example, earthworms.
Subject: Basic Chemistry
What are the different parts of an atom and how do they interact?
An atom is mostly empty space, but contains three types of particles: protons, neutrons, and electrons. Protons are positively (+) charged particles. Neutrons have no charge (Ø). The protons and neutrons make up the nucleus, which is at the center of the atom. Since like charges repel, the neutrons stop the protons from repelling each other too much. Electrons are negatively (–) charged. They orbit the nucleus in rings called "shells" because they are attracted to its positive charge. For the charges in an atom to balance, there must be an equal number of protons and electrons.
What are the similarities differences between mitosis and meiosis?
Mitosis and meiosis are both processes for cell division. They happen after the cell has replicated (made two copies of) its DNA. In both processes, cells undergo interphase, prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis. Somatic (non-reproductive) cells divide by mitosis, which produces two genetically identical "daughter cells". The chromosomes in the "daughter cells", like the "mother cell", are made of two chromatids (strands of double-helix DNA). Therefore, they are "diploid" (have two copies of the DNA). Sex cells divide by two rounds of meiosis, which is a little more complex than mitosis. There are two rounds of meiosis: meiosis I and meiosis II. Each round of meiosis contains all of the phases mentioned above. In prophase I (the first round of prophase), homologous pairs of chromosomes swap some of their DNA, which is known as "crossing over". This results in two genetically different "daughter cells". In the second round of meiosis, each new "daughter cell" receives one chromatid from each of the chromosomes. In the end, there are four genetically different "daughter cells" that have chromosomes made up of one chromatid. Therefore, they are "haploid" (have one copy of the DNA).
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