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Orlov [11]
2 years ago
15

Why are there holes in the ends of phloem tubes?

Biology
1 answer:
Diano4ka-milaya [45]2 years ago
5 0

There are holes in the end of the phloem tubes because Phloem consists of sieve tube cells and companion cells for conduction of food These sieve elements are placed end to end . At the the junction of two sieve elements there is a plate called sieve plates having circular pores.

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In 1980, Y. published an extended pedigree of family in which
nydimaria [60]

Answer:

Zero (0)

Explanation:

According to the given information the genotype of the woman with blood type "AB" would by I^AI^B. The genotype of the man with blood type O would be "ii". Here, the alleles I^A and I^B are dominant over the allele "i".

A cross between parents with genotype I^AI^B and ii would give 50% of children with I^Ai genotype and 50% of children with I^Bi genotype. The children with "I^Ai genotype" would have blood type "A" and the children with I^Bi genotype would have blood type "B". This couple is never likely to have any child with blood type "O" since the mother does not carry allele "i".

Cross: I^AI^B x ii = 1/2 I^Ai : 1/2 I^Bi

5 0
3 years ago
Under what circumstances does membrane transport always require energy?
kondor19780726 [428]
It requires energy when a substance must travel against a concentration gradient through the membrane
8 0
3 years ago
Which best describes Darwin's studies that led to the theory of evolution?
ddd [48]

Answer:

The answer is B, extensive research of an individual organism over many years.

Explanation:

The question is asking, what best describes Darwin's studies that led to the theory of evolution, it would be a lot of research over a long period of time. Think, if you were to do a school project, would you get your best results over a short or long period of time with little or a lot of evidence/research? So, B is the best answer, I believe.

(PLEASE BRAINLIEST)

8 0
3 years ago
Oct4 is an embryonic stem cell specific transcription factor. ESCs grown in petri dishes are fed media that contain basic fibrob
GarryVolchara [31]

Answer:

miR-223 inhibits the expression of the fibroblast growth factor (bFGF) gene, and thereby ESCs cells maintain their undifferentiated state .

Explanation:

Non-coding RNA (ncRNAs) are molecules that regulate gene expression, thereby playing important biological functions in cell differentiation, cell cycle, apoptosis, etc. MicroRNAs (miRNAs) are a type of ncRNAs capable of controlling gene expression patterns by regulating mRNA stability and by suppressing their translation into proteins. It has been shown that miRNAs function by imperfectly base-pairing with the 3′ UTR of target mRNAs (Pillai et al. 2005).

Citation:

R. S. Pillai, S. N. Bhattacharyya, C. G. Artus,   T.  Zoller, et al. (2005). Inhibition of translational initiation by Let-7 MicroRNA in human cells. Science, 309(5740), 1573-1576.

4 0
2 years ago
What does not deliver deoxygenated blood to the heart?
FrozenT [24]

Answer:

Pulmonary veins

Explanation:

In the circulatory system, the heart is responsible for for pumping oxygenated blood throughout the body and deoxygenated blood to the heart.

Normally all veins carry deoxygenated blood. However the pulmonary vein is the only vein that carries oxygenated blood.

They carry oxygenated blood from the lungs to the heart.

However the Superior and inferior vena cava are responsible for delivering deoxygenated blood to the heart.

4 0
3 years ago
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