# Connective Tissues: Blood, Cartilage and Bone

Biology I · Cells and Tissues · https://tryals.app/learn/biology-i/connective-tissues-blood-cartilage-and-bone

## Where the Matrix Is the Tissue

Connective tissue inverts the epithelial arrangement. Where epithelium is cells with almost no matrix, connective tissue is **mostly matrix** with cells scattered through it, and the matrix is what determines the tissue's properties.

The matrix has two components. **Fibres**: **collagen** for tensile strength, **elastic** fibres for recoil, **reticular** fibres for fine networks. And **ground substance**, which ranges from liquid to rubbery to solid.

That range produces a strikingly diverse family from one design:

| Tissue | Ground substance | Property |
|---|---|---|
| Loose connective | Viscous gel | Packing, flexible |
| Dense regular | Packed parallel collagen | Tensile strength in one direction |
| Adipose | Cells dominate | Energy store, insulation |
| Cartilage | Firm rubbery gel | Resilient, avascular |
| Bone | Mineralised with calcium phosphate | Rigid, vascularised |
| Blood | Liquid plasma | Transport |

**Blood** is connective tissue with a liquid matrix, surprising until you notice it fits the definition exactly. Plasma is about 55 % of volume, and formed elements about 45 %, the **haematocrit**. Red cells carry oxygen and, in mammals, lose their nucleus to make room for haemoglobin. White cells defend. Platelets are cell fragments that clot.

**Cartilage** is avascular, so its chondrocytes are fed by diffusion through the matrix. This is precisely why cartilage heals so poorly, no blood supply means no rapid delivery of cells or materials, which is why knee cartilage injuries are so persistent.

**Bone** solves that problem. Its mineralised matrix is rigid, but it is penetrated by blood vessels running in **Haversian canals**, with osteocytes sitting in small cavities connected by fine channels. Bone therefore heals well and, more remarkably, **remodels** continuously: osteoblasts build, osteoclasts break down, and the balance responds to mechanical load. Bone is a tissue that redesigns itself according to how it is used, which is why weight-bearing exercise strengthens it and why astronauts lose bone mass.

> **Common pitfall:** treating cartilage as simply "soft bone". They are separate tissues with different matrices, and the functional difference that matters most is vascularity: bone is supplied and heals; cartilage is not and does not.

## Practice questions

6 of this lesson's 11 practice questions, with answers. The full set is in the app.

### 1. Why does cartilage heal so much more slowly than bone?

A. Chondrocytes are post-mitotic and unable to divide to replace lost tissue
B. Its rubbery ground substance prevents osteoblasts from depositing collagen
C. Cartilage lacks sensory nerve fibres, so healing responses are not triggered
D. Cartilage is avascular, so cells and materials cannot be delivered rapidly

**Answer:** D. Cartilage is avascular, so cells and materials cannot be delivered rapidly

**Why:** Cartilage has no blood supply, its chondrocytes are fed by slow diffusion through the matrix, so repair materials cannot be delivered quickly. Bone is well vascularised and heals comparatively fast, which is why a broken bone mends in weeks while damaged knee cartilage may never fully recover.

Page: https://tryals.app/practice/biology-i/connective-tissues-blood-cartilage-and-bone/why-does-cartilage-heal-so-much-more-slowly-than-bone

### 2. A blood sample has a haematocrit of 42 %. If the sample is 5.0 mL, what volume of plasma does it contain, in mL, to one decimal place?

**Answer:** 2.9 (within ±0.1)

**Why:** Plasma is $100 - 42 = 58\%$, so $5.0 \times 0.58 = 2.9$ mL. Plasma is mostly water but carries proteins, nutrients, wastes and hormones, it is the transport medium the whole tissue exists to move.

Page: https://tryals.app/practice/biology-i/connective-tissues-blood-cartilage-and-bone/a-blood-sample-has-a-haematocrit-of-42-if-the-sample-is-5-0-ml

### 3. In connective tissues, matrix determines functional properties rather than the cellular content. How does this structural principle explain why bone can actively remodel under mechanical stress while cartilage cannot?

A. A mineralised matrix permits vascular channels that supply remodelling cells
B. Osteocytes actively secrete mineral whereas chondrocytes remain metabolically inert
C. Bone ground substance is fluid enough to allow osteoblasts to migrate freely
D. Cartilage matrix contains no fibrous network to resist external physical loads

**Answer:** A. A mineralised matrix permits vascular channels that supply remodelling cells

**Why:** Remodelling requires continuous nutrient delivery and cell turnover via blood vessels, which bone's rigid architecture accommodates through canal systems. Cartilage's avascular, gel matrix relies solely on slow diffusion, preventing rapid cellular adaptation.

Page: https://tryals.app/practice/biology-i/connective-tissues-blood-cartilage-and-bone/in-connective-tissues-matrix-determines-functional-properties-rather

### 4. Sort each tissue by the state of its ground substance.

**Answer:**

- Liquid matrix: Blood
- Firm gel matrix: Cartilage
- Mineralised solid matrix: Bone

**Why:** All three are connective tissues, differing only in their matrix, liquid, rubbery gel and mineralised solid. Blood counts because the definition is about matrix dominance, not about rigidity.

Page: https://tryals.app/practice/biology-i/connective-tissues-blood-cartilage-and-bone/sort-each-tissue-by-the-state-of-its-ground-substance

### 5. Which statements about blood as a connective tissue are correct?

A. Its cells are suspended rather than in contact
B. It is avascular, like cartilage
C. Mammalian red blood cells lose their nucleus at maturity
D. It has a liquid matrix called plasma

**Answer:** A. Its cells are suspended rather than in contact; C. Mammalian red blood cells lose their nucleus at maturity; D. It has a liquid matrix called plasma

**Why:** Liquid matrix, suspended cells and enucleate red cells are all correct. Calling blood avascular is a category error: it is what fills the vessels, and losing the nucleus is what makes room for more haemoglobin.

Page: https://tryals.app/practice/biology-i/connective-tissues-blood-cartilage-and-bone/which-statements-about-blood-as-a-connective-tissue-are-correct

### 6. Arrange these steps in the order a bone fracture heals.

**Answer:**

1. A blood clot forms at the fracture site
2. Inflammatory cells arrive and clear debris
3. A soft cartilaginous callus bridges the gap
4. The callus is replaced with bone
5. The bone is remodelled back toward its original shape

**Why:** Healing depends on bone’s vascularity from the first step, the clot brings the cells that begin repair. The temporary cartilaginous callus is later replaced and then remodelled, which is why a healed fracture can eventually become almost invisible.

Page: https://tryals.app/practice/biology-i/connective-tissues-blood-cartilage-and-bone/arrange-these-steps-in-the-order-a-bone-fracture-heals