【BIO】== Q&A ==

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【BIO】== Q&A ==

帖子 由 Giraffe 于 周六 七月 25, 2009 12:50 pm

explain what happens in an animal cell where there is insuffiicent oxygen for aerobic respiration?


ANSWER

When there is insufficient oxygen for aerobic respiration,
glycolysis can stil take place in the cytoplasm of the animal cell
and produce pyruvate.
however,the pyruvate molecule will not enter the Krebs cycle
and the electron transport system will not function.
Instead,anaerobic respiration occurs whereby the pyruvate molocule will accept back the hydrogen atoms
from the reduced NAD
and be converted into lactate

if anaerobic respiration continues,
lactate will accumulate and cause muscle cramping.
when oxygen is sufficient,
the lactate can be broken down and excreted.
as glucose is not completly broken down in anaerobic respiration,
the energy yield is very little where only 2 ATP molecules are produced.


由Giraffe于周四 八月 12, 2010 10:43 am进行了最后一次编辑,总共编辑了1次

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回复: 【BIO】== Q&A ==

帖子 由 Giraffe 于 周六 七月 25, 2009 12:50 pm

explain why in the absence of oxygen
1.no ATP synthesis occurs in mitochondria?
2.pyruvate is reduced to lactate?


1.
in the absence of oxygen
no ATP synthesis occurs in mitochondria
due to oxygen's role as final acceptor of hydrogen atoms in the ETS.
as there is no oxygen to accept the hydrogen atoms,
oxidative phosphorylation does not occurs to form any ATP.

2.
in the absence of oxygen
pyruvate is redueced to lactate as it accepts directly the hydrogen atome on the reduced NAD from the
glycolysis stage since there is no
oxygen to accept the hydrogen atoms.

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回复: 【BIO】== Q&A ==

帖子 由 Giraffe 于 周六 七月 25, 2009 12:51 pm

why should the diameter of mitochondria remain fairly constant when the length is so variable?


for rapid diffusion of molecule between cytoplasm and mitochondria

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回复: 【BIO】== Q&A ==

帖子 由 Giraffe 于 周六 七月 25, 2009 12:51 pm

WHat are the function of blood?(7m)


@transport digested food from the digestive tract to cells and tissues
@transport CO2 from the tissues and cells to lunngs
@transport O2 from the lungs to the cells as tissues
@transport excretory waste from the cells and tissues to the kidney
@transport of hormone from the endocrine gland to the target cells
@help to distribute body heat in the regulation of body temperature
@help in the body defence aganst diseases

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回复: 【BIO】== Q&A ==

帖子 由 Giraffe 于 周六 七月 25, 2009 12:51 pm

Explain how nucleus, endoplasmic reticulum, Golgi apparatus, lysosom and plasma membrane are inter-related.

(15m)


-Nucleus contains DNA, the genetic information for synthesis of mRNA
and proteins including enzymes .Therefore, nucleus is related to
endoplasmic reticulum(ER), Golgi apparatus and lysosome directly or
indirectly through mRNA and proteins.

-Beside, nucleus is the site where ribosomes are formed in the
nucleolus. From the nucleus both mRNA and ribosomes move out into
cytoplasm through nuclear pores.

-Nucleus is related to ER as the outer membrane of the nucleus can
extend to form ER. ER is a system of tubules and flattened sacs
(cisternae) for internal transport and storage of materials.

-Rough ER is formed with ribosomes from the nucleus and attached to it su***ce.
-With the help of genetic information in the form of mRNA , proteins are produced by the ribosomes and enter through ER.
-Some of the proteins produced also get lodged into the inner wall of the ER. Most of the proteins are enzyme.

-The ER is related to Golgi apparatus as break away sacs from ER can form Golgi apparatus.
-Golgi apparatus can process the proteins within its cisternae to form glycoprotein mainly mucus.
-Golgi apparatus with enzymes on its internal wall can synthesized lipid and cell wall carbohydrate in plant cells.
-The proteins including enzymes, glycoproteins, cell wall carbohydrates
and lipids are packaged in the form of vesicles by Golgi apparatus.

-Some of the vesicles produced by Golgi apparatus contain purely hydrolases and combine to form lysosomes.
-The lysosomes may be used to digest old organelles or even the whole
cells including nucleus, ER and Golgi apparatus when worn out.

-Some of the packaged materials in the vesicles are meant for export out of the cell and exocytosised.
-When that occurs, the walls of the vesicles form the plasma membrane.
-Such cells that produce a lot of secretions would have its plasma
membrane constantly expanding. It is regulated by breakage of the
plasma membrane or the whole cell is digested by autophagy by its own
lysosome so new cells are formed for replacement.

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回复: 【BIO】== Q&A ==

帖子 由 Giraffe 于 周六 七月 25, 2009 12:51 pm

Compare plants from the Division Pteridophyta with plants from the Division Bryophyta.
(12m)

Similarities between Pteridophyta and Bryophyta

Multicellular

Autotrophs

Showing alternation of generation

Need external water for fertilization

Differences
Pteridophyta

Vegetative structure --stem, leaves and roots

Roots for anchorage and absorption of water

Vascular plant, have xylem and phloem for transporting water and nutrients

Sporophyte dominant

Gametophyte of sporophyte independent of each other

Sporangium is clusters under the leaves

Bryophyta

Thallus or simple leaf-like

Structure without roots, Rhizoids for anchorage only

Non-vascular plants, water and nutrients transported by diffusion

Gametophyte dominant

Sporophyte depending on gametophyte

Sporangium in capsules at end of stalks

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回复: 【BIO】== Q&A ==

帖子 由 Giraffe 于 周六 七月 25, 2009 12:51 pm

jelaskan bagaimana tumbuhan dapat mengelakkan berlakunya pendebungan sendiri?
10m


@having dicliny flower
i.e.the stamen and the carpel are in seperate flower
@monoecious-both male and female flower
are on the same plant
eg:maize
@dioecious-male and female flower are on dfren plants
e.g.papaya
@self-sterility
the flower cannot be fertilised by its own pollen grains,the stigma dries off and fall off
e.g.;orchid
@dichogamy
the anther and stigma matured at dfren time
@protogyny-the female parts of the flower matured 1st
e.g.palm
@protandry-the male parts of the flower matured 1st
e.g.hibiscus
@heterostyly
the flower have dfren length of filament and styles
@herkogamy
the floral part becomes a fence/barrier of self-pollination
e.g.orchid,Iris

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回复: 【BIO】== Q&A ==

帖子 由 Giraffe 于 周六 七月 25, 2009 12:51 pm

Production of thyroxine(5m)


@is produced by the thyroid gland
@is made up of follicle cells
@iodin is required for thyroxine production
@the follicle cells contains the precursor to thyroxine
ie thyroglobulin
@the hydrolytic enzyme that hydrolyses protein from the epithelial cells hydrolyses thyroglobulin to produce thyroxine
@thyroxine produced then enter the blood,transport into target organs

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回复: 【BIO】== Q&A ==

帖子 由 Giraffe 于 周六 七月 25, 2009 12:51 pm

function and action of thyroxine(7m)


@the hormone thyroxine inhibit the release of TSH hormone
@via the negative feedback mechanism
@the producyon of thyroxine in turn is controlled by TSH
@when the body is at rest,thyroxine regulate the basal metablolic rate(BMR)
@thyroxine in general control the metabolic rate of body
@increase in the release of thyroxine,increases the BMR
@it can control growth&development by controlling the growth&differenciation of the cells

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回复: 【BIO】== Q&A ==

帖子 由 Giraffe 于 周六 七月 25, 2009 12:52 pm

describe the stucture of DNA.(9m)


@diagram of DNA
@consists of nucleotide/phosphoric acid+nucleoside
@the 4 N2 bases are:purines~adenine and guanine
pyrimidines:thymine and cytosine
@the nucleotide consists of 2 chaiins
@in a double helix structure
@the base pairing is specific:
a)adenine pair with thymine
b)guanine pair with cytosine
@the N2 bases are joined by hydrogen bond
@2 hydrogen bonds joined A and T while
3 hydrogen bonds joined G and C
@the sugar and the phosphate forms a backbone of the molecule
@the phosphate is attached to the sugar by phosphodiesther bond

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回复: 【BIO】== Q&A ==

帖子 由 Giraffe 于 周六 七月 25, 2009 12:52 pm

explain the rolr of NAD and oxygen in oxidative phosphorylation?(8m)


-In glycolysis, glycealdehyde-3-phosphate is oxidised, hydrogen atoms are removed, NAD is reduced to become NADH.
-In the link reaction, NAD oxidised 2C fragment forming acetate in form of NADH.
-In Kreb Cycle, isocitrate is oxidised to form oxalosuccinate. NAD is reduced to become NADH.
-malate is oxidised to regenerate oxaloacetate, and NAD is reduced to NADH.
-NADH transfers hydrogen atom to specific carriers on the inner membrane of mmitochondrion and are oxidised back to NAD.

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