【PEP】Senior High Biology, Selective Compulsory, Book 1: Cradle of Life — Comparing the Living Environments of Unicellular and Multicellular Organisms

Life first emerged in the turbulent primordial ocean. For unicellular organisms (such as paramecia), the ocean or pond water is both their home and a "supermarket" where they directly obtain nutrients and expel waste. Their connection to the external environment isdirect and transparent.

₂Metabolic WasteExternal Aquatic EnvironmentCapillaryInterstitial Fluid (Internal Environment)Inside a Multicellular Organism

The Evolutionary Logic: From "External Ocean" to "Internal Environment"

With the emergence of multicellular organisms, body size increased dramatically, burying the vast majority of cells deep inside the body where they could no longer directly contact the outside world. Thus, life evolvedthe internal environment(the extracellular fluid composed of blood plasma, interstitial fluid, lymph, etc.).

Openness: The internal environment is not closed off; rather, it maintains efficient material exchange with the outside world through the digestive, respiratory, circulatory, and urinary systems.
Integration: The extracellular fluid throughout the body is interconnected, forming an organic whole that collectively maintains the relative stability of physicochemical properties.
Dynamic Equilibrium: The internal environment mimics the constancy of the primordial ocean (temperature, pH, osmotic pressure), providing a sheltered "cradle" for cells and enabling complex life to break free from the constraints of harsh external conditions.

Embracing the Concept of Life

Recognize the characteristics of living systems — openness, integration, and dynamic equilibrium — and use these as a guide to analyze life phenomena. Regardless of external heat or cold, the homeostasis of the internal environment is a necessary condition for our normal life activities.

QUESTION 1

The internal environment is the immediate environment in which the body's cells live. Which of the following belongs to the internal environment?

Urine in the bladder

Fluid between brain cells

Air in the alveolar cavities

Digestive fluid in the small intestine lumen

QUESTION 2

After manual labor, the "blisters" that form on the palms naturally disappear. The reason is:

The fluid in the blister is mainly blood plasma, which has the highest protein content

The fluid is reabsorbed into the blood plasma or enters the lymphatic capillaries

Blister formation shows that substances in the internal environment are stationary

The fluid evaporates directly into the air through the pores of the skin

QUESTION 3

In the "Simulating pH Stabilization in Organisms" experiment, the behavior of liver homogenate most closely resembles:

Tap water, where pH changes drastically with the addition of acid or base

Phosphate buffer solution, where pH remains relatively stable

A strong acid solution, keeping pH at a consistently low level

Distilled water, where pH stays constant at 7.0

QUESTION 4

Regarding the physicochemical properties of extracellular fluid, which of the following statements is incorrect?

The osmotic pressure of blood plasma is mainly related to the content of inorganic salts and proteins

Over 90% of the osmotic pressure of extracellular fluid comes from Na⁺ and Cl⁻

The pH of normal human plasma is 7.35–7.45

Homeostasis of the internal environment refers to a state where physicochemical properties are constant and unchanging

QUESTION 5

Which of the following statements about blisters is incorrect?

Protein content is the highest among the components of a blister

Blisters are mainly formed by large amounts of water from plasma leaking into the interstitial fluid

Blisters disappear on their own because the fluid inside can seep into blood capillaries and lymphatic capillaries

The formation and disappearance of blisters indicate that substances in the internal environment are constantly being renewed