【PEP】High School Biology, Compulsory Book 1: Why Can't Cells Grow Indefinitely Large?

Have you ever wondered why there are no "single-celled organisms" as large as a mountain in nature? The material basis of life tells us that cell size is strictly constrained by physical and biological laws. The core reason why cells cannot grow indefinitely is thelimitation of the relative surface area (surface area-to-volume ratio, S/V), as well as the nucleus's limited ability to control an overly large volume of cytoplasm.

1. The Red Line of Material Exchange Efficiency

Cellular life activities depend on the supply and utilization of energy. Like a busy factory, cells capture energy throughphotosynthesis or release energy through respiration, which involves the transmembrane transport of large quantities of substances. When a cell's volume increases, its volume (V) grows cubically, while its surface area (S) only grows quadratically. This means that the smaller the relative surface area, the lower the efficiency of material exchange with the external environment (e.g., the transport of $H_2O$, glucose, and $O_2$).

2. The Control Efficiency of the Nucleus

The nucleus is the "brain" of the cell. The amount of genetic material within a single nucleus is limited. If the cell becomes too large, it takes longer for the "instructions" from the nucleus to reach the cell's periphery, making it impossible to precisely regulate complex biochemical reactions, such as specific enzymatic reactions and theconversion between ATP and ADP. Therefore, the growth of an organism mainly relies on increasing the number of cells through cell division, a process known ascell proliferation.

QUESTION 1

In the pigment separation experiment on filter paper, how many pigment bands are there on the filter paper strip? What is their order from top to bottom?

4 bands; carotene, xanthophyll, chlorophyll a, chlorophyll b

4 bands; chlorophyll a, chlorophyll b, carotene, xanthophyll

2 bands; chlorophyll, carotenoids

3 bands; carotene, xanthophyll, chlorophyll

QUESTION 2

Why do the nuclei of differentiated animal somatic cells still retain totipotency?

Because the nucleus contains the high-energy phosphate compound ATP

Because the nucleus contains the complete set of genetic material required for the growth, development, and heredity of that species

Because the nucleus can divide indefinitely for cell proliferation

QUESTION 3

Evaluate the following statement about chloroplast structure and function: Plant leaves appear green because chloroplasts absorb green light.

True

False

QUESTION 4

If $CO_2$ containing $^{14}C$ is used to trace the transfer pathway of carbon atoms in photosynthesis, what should the pathway be?

$CO_2 \rightarrow C_5 \rightarrow (CH_2O)$

$CO_2 \rightarrow C_3 \rightarrow (CH_2O)$

$CO_2 \rightarrow ATP \rightarrow (CH_2O)$

QUESTION 5

Which of the following statements about cell proliferation is incorrect?

Cell proliferation is the basis for an organism's growth, development, reproduction, and heredity

The process by which cells increase in number through division is called cell proliferation

The larger the cell volume, the higher the efficiency of material exchange, which is therefore beneficial for proliferation