<span>Plant and animal cells have different structures. One structural difference of plant cells and animal cells is the presence of the plant cell’s </span>cell wall,<span> specialized plastids and a large central vacuole which are not found within animal cells.
Another difference is the garbage disposal of each cell. Centrosomes and lysosomes are found in animal cells but both do not exist within plant cells. The animal cell’s garbage disposal takes place in the lysosome while garbage disposal of plant cells takes place in the vacuole.</span>
Answer: A: Its fertile oases enabled farmers to grow enough food for themselves and for sale.
Explanation: The Arabia region is a region located within the Arabian desert. A desert is an area of extreme heat, often dry weather condition with barren lands that cannot support agriculture and food production. An oases on the other hand is a region of luscious, cultivate-able land within a desert.
Food is one of the most important basic needs of man and hardly can anyone survive without food for more than twenty days. Hence, the presence of oases within the otherwise dry environment of the Arabia region is a major protection against death from hunger.
Taking a closer look at other options, none of them guarantees food supply and income to the Arabia region unlike food production in oases. Hence, the fertile oases is really the most important factor that serves as protection in the region's history.
Correct option: A
Answer:
The most appropriate answer would be option B.
The flaw in their reasoning is that they compared different molecules in a different set of organisms.
For example, they compared the DNA of lizard A and B whereas they compared the RNA of lizard B and C.
In addition, the mutation rates of different molecules (DNA and RNA) are different and thus, comparison of DNA in one set of organism and comparison of RNA in another set cannot be used as the basis for the conclusion.
1. breeding of individuals that have genes for two different characteristics:
DIHYBRID CROSS.
We call it a dihybrid cross when we are considering a cross between two different traits.
"di" means having two traits involved (for example, trait A and trait B), the "hybrid" means that each trait will have two different alleles (for gene A: A or a; for gene B: B or b), one is dominant and the other is recessive.
2. a grid system used to predict possible combinations of genes due to random fertilization: PUNNETT SQUARE
The Punnett square is a grid system that helps us predict an outcome of a cross or a breeding experiment. We this, we can determine the probability of an offspring having a particular genotype.
This is very useful when we are considering more than one gene, making it less confusing.
3. a condition in which both alleles are dominant: CODOMINANCE
Tere are alleles that have the capacity of dominating at the same time, and when an organism is heterozygotic, both alleles are expressed.
For example, a white chicken(WW) crossed with a black chicken (BB): 100% of the offspring being WB. With this genotype, they have black feathers and white feathers. It's not a blend of colors, but a case where both are expressing.
4. when more than two alternatives exist for a gene: MULTIPLE ALLELES
Mendel thought that only two possible alternatives could exist for a gene, but there are cases that have more than 3 possibilities. Some of those can be really popular in a population while others not so much.
This happens with rabbit's fur. They can be black, brown, grayish,
Himalayan patterning or white fur.
5.a condition in which neither pair of alleles is dominant or recessive, so the traits blend in the phenotype: INCOMPLETE DOMINANCE
Some alleles are not completely dominant, and when that's the case the phenotype of a heterozygous organism will be a mix between the phenotypes of its homozygous parents.
For example:
plant 1: RR -red
plant 2: rr-white
By crossing this plants we will obtain 100% of the offspring with a color mix: pink.(genotype: Rr)
Red and white are not completely dominating so it results in a blend of colors.
Answer:
E) Improve membrane fluidity
Explanation:
Cholesterol constitutes the basic structural element of the skeleton of cell membranes. Without their reinforcement, the membranes would become extremely fluid and lose their consistency. Cholesterol is found in the esterified membranes in its hydroxyl group (OH): with fatty acids, mainly oleic and linoleic, or as cholesterol sulfate. The cholesterol-sulfate polar group is disposed on one of the faces of the membrane that interacts with other polar groups in that area, while its bulky hydrophobic portion is embedded between the apolar parts of the lipids that form the membrane skeleton and They fulfill many other functions, among which the reduction in the permeability of protons and sodium ions, and their participation in signal transmission. Cholesterol is also essential in phagocytosis processes carried out by cells to capture many nutrients and, in general, for the function of cleaning up organic waste produced by macrophages.
The membranes must have a fluid structure so that the integrated proteins can move "horizontally" to interact with their ligands and with other proteins. The fluidity is given by unsaturated fat. With the excess of saturated fat, the membranes become rigid, but only with the necessary unsaturated fat the membranes are extremely fluid and very sensitive to temperature changes. Cholesterol stabilizes the structure of the membranes; In order for them to have the correct structure, they must have the correct proportions of saturated, unsaturated fats and cholesterol. The membranes produced in the laboratory without cholesterol are unstable to temperature changes, drastically modifying their fluidity against the small temperature changes that occur in the physiological range.
In addition to its functions in cell membranes, cholesterol is an important product that metabolism uses as a raw material to make other compounds:
*Bile salts
*Sex hormones
*Hormones of the adrenal cortex (corticosteroids)
*Vitamin D (Calciferol)
