【Shanghai Edition】Junior High School Science, Grade 8, Semester 1: The Command Center of Life

The Grand Blueprint of Life: The Nucleus

If we compare a cell to a precisely operating city, thenthe nucleusis the city’s “command center” and “classified archive.” Here lies the ultimate instructions governing biological development and traits—deoxyribonucleic acid (DNA). It is the helmsman of life activities, guiding cellular metabolism, growth, and reproduction.

Structural Logic and Unity

Material Carrier: Genetic information normally appears as thread-likechromatin, and during division tightly coils intochromosomes. Human somatic cells consistently contain23 pairs of chromosomes.
Essence of Life: Deoxyribonucleic acid (DNA) exists in the nucleus, and DNA is the primary genetic material of the cell.
Division Process: Cell division refers to one cell splitting into two. During division, the nuclear material first splits into two, forming two new nuclei; then the cytoplasm and cell membrane are divided into two parts.

Blueprint Analogy

The case of cloned sheep Dolly proves that the nucleus acts like an architectural blueprint. No matter where this blueprint is placed (in a recipient cell), the final building (biological traits) must be constructed according to the plan.

QUESTION 1

In the amoeba cutting experiment, why does the fragment without a nucleus eventually die?

Cytoplasm is the primary genetic material

The nucleus is the control center of cellular life activities

The nucleus provides all the energy required by the cell

Amoebas can survive for long periods without a nucleus

QUESTION 2

Which ewe does cloned sheep Dolly most closely resemble in appearance?

The ewe that provided the enucleated egg cell

The surrogate mother

The ewe that provided the cell nucleus

QUESTION 3

Which of the following correctly describes the sequence of cell division?

Cytoplasm divides first, nucleus later

Nucleus and cytoplasm divide simultaneously

The nucleus divides first into two, followed by division of the cytoplasm and cell membrane

QUESTION 4

How many pairs of chromosomes do normal human somatic cells contain?

23 chromosomes

23 pairs

46 pairs

QUESTION 5

What is the main genetic material in the nucleus?

Proteins

deoxyribonucleic acid (DNA)

Ribonucleic acid (RNA)

Deep Dive: Replication and Differentiation of Life

Comprehensive Analysis Based on Nuclear Function and Developmental Logic

The human body contains various types of cells with distinct functions—such as nerve cells responsible for signal transmission and muscle cells for movement. Despite their vastly different appearances, they all originate from a single fertilized egg.

1. Why do cells in different parts of the human body differ greatly, yet all contain 23 pairs of chromosomes in their nuclei?

Answer:
Because all human somatic cells are produced through cell division from a single fertilized egg. During division, chromosomes replicate and are evenly distributed to two daughter cells, ensuring stability of genetic information. Although different cells vary in function due to differentiation, their core genetic foundation (blueprint) remains identical.

2. Describe the morphology and structure of cell groups in nervous and muscular tissues. What changes do cells undergo during the process of forming an organism from a single fertilized egg?

Answer:
Nerve cells have uneven extensions, appearing star-shaped, which aids impulse conduction; muscle cells are typically spindle-shaped or fibrous, enabling contraction. From a fertilized egg to a full organism, cells undergo division (increased number), growth (increased size), and differentiation (changes in shape, structure, and function to form tissues).

3. Based on Dolly’s case, if a nucleus from a nerve cell were implanted into an enucleated egg cell, could a complete individual containing muscle tissue theoretically develop?

Answer:
Theoretically yes. Since the nucleus of a nerve cell contains the entire set of genetic information (23 pairs of chromosomes/DNA blueprint) of the organism, these instructions cover the creation of all tissues—including muscle—and, given suitable conditions, can guide the development of a complete organism.