أسئلة تدريبية في علم الأحياء – الصف الثاني عشر – المنهج اللبناني

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سجّل على edurise.me واشترك (10 دولارات شهرياً) لتتدرّب على كل فصول علم الأحياء للصف الثاني عشر، وتقدّم الامتحانات المؤقّتة وتتابع تقدّمك.

Question 1

Fertilization restores:

Accepted Answer

the diploid number of chromosomes. n (spermatozoon) + n (oocyte) → 2n (zygote).

Question 2

Which pathway do spermatozoa follow?

Accepted Answer

seminiferous tubule → epididymis → vas deferens → urethra. Sperm are made in the tubules, mature in the epididymis and are carried by the vas deferens to the urethra.

Question 3

Drosophila with red eyes is crossed with one with purple eyes. All 53 offspring have red eyes. What was the genotype of the parent with red eyes?

Accepted Answer

Pr//Pr. Test cross: the purple eyes parent gives only pr/ gametes; all offspring dominant → the tested parent gave only Pr/ gametes: Pr//Pr.

Question 4

Two heterozygous Drosophila (Vg//vg) are crossed. What is the probability that an offspring shows vestigial wings?

Accepted Answer

1/4. Vg//vg × Vg//vg: P(vg//vg) = 1/2 × 1/2 = 1/4.

Question 5

Replacing one nucleotide by another is a:

Accepted Answer

substitution. One nucleotide is exchanged for another; the reading frame is kept.

Question 6

Mutations are said to be random because:

Accepted Answer

they do not occur in response to the needs of the organism. A mutagen raises the frequency of mutations but does not choose which gene mutates.

Question 7

The gene pool of a population is:

Accepted Answer

all the alleles of all its individuals. Frequencies of these alleles describe its genetic diversity.

Question 8

A sample of 1000 individuals contains 823 A//A, 111 A//a and 66 a//a. What is the frequency of genotype A//a?

Accepted Answer

0.111. Genotype frequency = 111 / 1000 = 0.111.

Question 9

Which technique of prenatal diagnosis carries no risk for the fetus?

Accepted Answer

ultrasound. Ultrasound is non-invasive; chorionic villi (10–12 weeks) and amniotic fluid (15–17 weeks) give fetal cells for a karyotype (chromosomes) or DNA analysis (alleles).

Question 10

The photograph of chromosomes classified by pairs is called:

Accepted Answer

a karyotype. Chromosomes are classified by size and banding into 23 pairs.

Question 11

A molecule able to trigger an immune response is:

Accepted Answer

an antigen. The self is defined by markers (HLA, blood groups); the non-self includes foreign molecules and the modified self, recognised through their epitopes.

Question 12

The marker CD4 is carried by:

Accepted Answer

TH (T4) lymphocytes. Bone marrow produces all immune cells; B mature there, T in the thymus (primary organs). Lymph nodes, spleen and tonsils (secondary organs) host the encounter with antigens. Plasma cells secrete antibodies; Tc destroy infected cells.

Question 13

Which is NOT one of the four local signs of inflammation?

Accepted Answer

paleness and cooling of the area. Inflammation: vasodilation (redness, heat), permeability (swelling), mediators on nerve endings (pain); phagocytes arrive by diapedesis and chemotaxis. Immediate and non-specific.

Question 14

In an Ouchterlony test, an arc of precipitation shows:

Accepted Answer

the formation of antigen–antibody complexes. Vaccination: antigen → memory (active, lasting, delayed). Serotherapy: antibodies (passive, immediate, short). Antibody specificity is used in ELISA, Western blot and Ouchterlony tests.

Question 15

HIV mainly infects:

Accepted Answer

cells carrying CD4 (TH lymphocytes and macrophages). HIV: retrovirus (RNA → DNA by reverse transcriptase), gp120 binds CD4 of TH and macrophages; phases: primary, asymptomatic, AIDS (CD4 < 200/mm³).

أسئلة علم الأحياء الصف الثاني عشر مع الحل

15 سؤالاً تدريبياً في علم الأحياء – الصف الثاني عشر

1. Fertilization restores:

2. Which pathway do spermatozoa follow?

3. Drosophila with red eyes is crossed with one with purple eyes. All 53 offspring have red eyes. What was the genotype of the parent with red eyes?

4. Two heterozygous Drosophila (Vg//vg) are crossed. What is the probability that an offspring shows vestigial wings?

5. Replacing one nucleotide by another is a:

6. Mutations are said to be random because:

7. The gene pool of a population is:

8. A sample of 1000 individuals contains 823 A//A, 111 A//a and 66 a//a. What is the frequency of genotype A//a?

9. Which technique of prenatal diagnosis carries no risk for the fetus?

10. The photograph of chromosomes classified by pairs is called:

11. A molecule able to trigger an immune response is:

12. The marker CD4 is carried by:

13. Which is NOT one of the four local signs of inflammation?

14. In an Ouchterlony test, an arc of precipitation shows:

15. HIV mainly infects:

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